The Portuguese's importance to Massimiliano Allegri's squad was underlined on Wednesday when he was left out of the starting line-up for the first time this season.
Juve found themselves a man and 2-1 down away at Atalanta but Ronaldo came off the bench to preserve his new club's unbeaten record with a late leveller.
With that in mind, Goal looks back through the history books to see if any former overseas superstar has ever made such an instantaneous impact on Serie A.
The striker initially found goals hard to come by at the Artemio Franchi, netting only three times by the end of December, but he ended his first season in Serie A with a creditable 13, as a weak Viola side finished 12th.
'Batigol', as he came to be known, struck 16 times during his second campaign but that was not enough to save Fiorentina from the drop.
However, even though Batistuta had established himself as one of the top strikers in Serie A, he resisted offers from elsewhere to help the club secure an immediate return to the top flight, thus earning himself iconic status in Florence.
Batistuta continued to score freely for Fiorentina but despite some near misses, it was only after leaving to join Roma in 2000 that he won a long overdue Scudetto.
AC Milan broke the transfer fee world record in 1987 by signing Ruud Gullit from PSV for approximately £6 million but the Dutchman initially took time to settle at San Siro, struggling with the Italian language and only scoring two goals during the first half of the season.
However, the forward improved from January onwards, and ended up with nine goals to his name as the Rossoneri claimed their first Scudetto since 1979.
Despite some injury issues, Gullit would go on to become a legend at Milan, whom he helped win back to back European Cups, even scoring twice in the 1989 final against Steaua Bucharest.
Despite widespread interest in Kaka's services, AC Milan managed to snap up the Sao Paulo star in 2003 for just €8.5m, which president Silvio Berlusconi rather prophetically described as "peanuts"!
The attacking midfielder was the revelation of the Serie A season. Kaka had only scored twice by the winter break but he was proving a wonderful creative force, replacing Rui Costa in the starting line-up, and the goals began to follow in the New Year.
Indeed, he ended his debut campaign with 10 in total and was named Serie A Player of the Year for playing such a pivotal role in Milan's title triumph.
Essentially, Kaka was well on his way to becoming one of the finest players ever to grace Italy's top flight.
If Ronaldo's decision to join Juve was a surprise, Diego Maradona's move to Napoli rocked the footballing world to its very core.
The Partenopei had never even won the Scudetto yet managed to sign the Argentine for a world-record fee from Barcelona in 1984.
Maradona was greeted as a messiah in Naples and certainly achieved God-like status by leading Napoli to two Serie A title triumphs during his six-year stay at the San Paolo.
He did take time to prove his worth, netting only three times before the turn of the year, but that was hardly surprising, given he joined a team coming off the back of a 12th-placed finish.
However, he soon made his genius felt and ended his first campaign in Italy with 14 goals, which saw him rank third in the race for the Capocannoniere, just four behind victor Michel Platini.
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Even at the time, it was a steal. As Juve president Gianni Agnelli famously put it, "We've paid for a slice of bread (an idiom for 'pittance' in Italian) and they've given us foie gras!"
He wasn't wrong either.
Platini started slowly in Turin, only striking four times by Christmas. However, the France No.10 finished with 16 goals to take the first of three consecutive Capocannoniere awards, and three consecutive Ballons d'Or.
Inter took advantage of the breakdown in Barcelona's talks with Ronaldo's representatives over a new contract to make the Brazilian sensation the most expensive player in the world for the second time in just over a year, paying £19.5m ($27m) for his services.
The striker had terrorised defences in his one and only season at Camp Nou but he actually looked an even more complete forward at San Siro, quickly earning himself the nickname 'Il Fenomeno' for his goalscoring exploits.
Ronaldo struck nine times by the end of the December but added 16 during the second half of the season to finish with 25 in total, claiming the Serie A Player of the Year award in the process.
Sadly, that was to be as good as it got for Ronaldo at Inter because he suffered two serious knee injuries which meant he spent more time on the sidelines than on the pitch during his remaining four years at San Siro.
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The big question hanging over Andriy Shevchenko after his move to AC Milan in 1999 was whether he could replicate his impressive goalscoring feats at Dynamo Kyiv.
The Ukrainian posted an immediate response, netting seven times in his first seven Serie A appearances as he went about reaching the winter break with 10 goals to his name.
The striker proved even more prolific in the second half of the season as he finished with 24 goals to not only win the Scudetto for the Rossoneri, but also claim the Capocannoniere award in his first year at San Siro.
Shevchenko went on to become the second most prolific player in Milan's history and is still remembered as a club legend despite leaving for Chelsea in 2006 only to then return for an unsuccessful loan spell two years later.
Marco van Basten
Marco van Basten's Serie A career got off to the perfect start with the Dutch striker netting on his debut, in a 3-1 win at Pisa, but his first campaign was decimated by injury and he contributed just three goals in total to AC Milan's title triumph.
Once fully fit, though, Van Basten took the league by storm, racking up 19 goals in his second season at San Siro, and a further 10 during the Rossoneri's European Cup triumph, including a double in the final against Steaua Bucharest.
Van Basten would go on to prove himself one of the greatest centre-forwards the game has ever seen but, cruelly, he was forced to retire in 1995, aged just 31, after spending the previous two years sidelined by injury.
The Liberian only hit five goals by the turn of the year and finished the season with 11 in total but that was enough for him to finish top scorer for a title-winning Rossoneri side that not only boasted forwards of the calibre of Marco Simeone, Dejan Savicevic and Roberto Baggio.
Weah's all-round excellence had also resulted in him becoming the first African to win the Ballon d'Or.
He would enjoy a more prolific campaign in 1995-96, scoring 13 goals, including his iconic coast-to-coast strike against Verona, and he claimed a second Scuetto in 1999 but his first season in Serie A was undoubtedly his most impactful.
Many were mystified as to how the Zebrette had managed to stump up the cash to sign the outstanding talent from the ridiculously gifted Brazil side that graced the 1982 World Cup.
However, despite calls for the Italian Football Federation (FIGC) to block the transfer, the No.10 was allowed to join Udinese, much to the joy and disbelief of their supporters.
Zico hit the ground running, netting six times in his opening four games, and had racked up nine goals by the turn of the year.
He eventually ended with 19 goals in Serie A but was beaten to the Capocannoniere award by Platini by a single strike.
Despite Zico's brilliance, and his productive partnership with Franco Causio, Udinese only finished ninth on account of their porous defence.
Zico's second season was worse, with Udinese coming home 12th, but he remains a legend in Udine, not least for turning the free-kick into an artform.
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Amusingly, Blackburn Rovers turned down the chance to sign Zinedine Zidane because they already had Tim Sherwood, while Newcastle didn't think that the elegant Frenchman was good enough to play in the Championship – let alone the Premier League.
That left the way clear for Juventus to sign Zidane in the summer of 1996 for just €3.6m and it quickly became obvious that the Bianconeri had got themselves a bargain.
The attacking midfielder was excellent in his first season in Turin. Never a prolific player, Zidane scored five times in total – thrice before the turn of the year – as Juve claimed the Scudetto and their No.21 was named Serie A Foreign Player of the Year.
Zidane was even better in his second season in Italy and he helped the Bianconeri retain the Scudetto but they again suffered heartbreak in Europe, beaten by Real Madrid in the 2008 Champions League final.
As it transpired, it would only be after joining the Spanish giants for a world-record fee in 2001 that Zidane would finally get his hands on the European Cup, in 2002.
Ronaldo the top-scoring superstar
Thus by the turn of the year in his first season in Serie A, Ronaldo has scored more league goals than all of the superstars in this list did during the same time period.
While some of these players played more than others and while some would argue that Serie A was of a higher standard during its heyday in the 1980s and 1990s, Ronaldo can certainly boast that his first six months in Italy have been a roaring success.