The Portugal international was shown his very first red card in Europe's premier club competition after he appeared to pull the hair of defender Jeison Murillo.
Indeed, he had to be helped from the turf after collapsing upon seeing the card, and took a number of minutes to leave the pitch.
UEFA assess cases on an individual basis, though they do institute an automatic one-match suspension for a straight red dismissal.
So how long will Ronaldo be banned for and what game - or games - will he miss?
What did Ronaldo do to get sent off?
After running into the box, Ronaldo and Murillo clashed, the defender claiming he was kicked by the 33-year-old.
Ronaldo reacted to that, raising his arm in protest, before appearing to scratch Murillo's head with his hand.
The moment that saw Cristiano Ronaldo see red— B/R Football (@brfootball) September 19, 2018
[🎥: U.S. only] pic.twitter.com/IB3ffZweXw
How we didn’t expect Cristiano Ronaldo’s Champions League debut for Juventus to end...— Football on BT Sport (@btsportfootball) September 19, 2018
⚪️ With a goal
⚪️ With a hat-trick
🔘 In tears
He’s received his first-ever red card in the competition 😮 pic.twitter.com/VbOqOAh07q
Murillo then squared up to the forward, and players from both teams were forced to intervene.
Referee Felix Brych consulted the official behind the goal, and a decision was taken to send Ronaldo off, leaving him in tears.
You can watch the incident in the videos above.
Will Ronaldo miss Juventus' game against Man Utd?
A fairytale return to Old Trafford remains on the cards on October 23 after UEFA confirmed that Ronaldo will only be banned for one Champions League game.
That means the only game he is certain to miss is Juve's next encounter, against Young Boys, on October 2 in Turin.
Ronaldo was unable appeal his ban, but faces an anxious wait to see if that suspension will be extended by UEFA.
Game Ronaldo will miss
|Oct 2||Young Boys||Allianz Stadium, Turin|
There was a possibility that it might have been extended to two games, meaning he would have had to sit out the Old Trafford clash.
Former Premier League referee Mark Clattenburg believes Ronaldo's red card was harsh - he claims he would have shown both Murillo and the Portuguese a yellow, and awarded Valencia a free-kick - and thinks a one-match ban will suffice.
Writing in the Daily Mail, he said: "The contact looked very slight and I cannot see how the additional assistant, standing some 20 yards away, could deem it violent conduct.
"If I had been officiating this game, I would have given Valencia a free-kick and shown a yellow card to each player. Ronaldo will serve a one-match ban but anything more would be harsh."
Reaction to Ronaldo's red card vs Valencia
Ronaldo's sending off sent social media into a frenzy, with Twitter users across the globe either mocking the crying superstar or criticising the referee.
Indeed, one user claimed that the decision was "one of the most ridiculous sendings off ever".
Leonardo Bonucci indicated that his team-mate was left "angry" at the decision, while Juve boss Massimiliano Allegri believes VAR would have saved the star .
Miralem Pjanic went one step further, despite scoring the two penalties that won Juve the game, and insisted that the red card was "absurd".
"Football is a strange game. We could have been 4-0 up after the opening period, then came that absurd sending off," Pjanic said, via the club's website.
“That’s supposed to be a red!?” he exclaimed when shown footage of the action by DAZN .
“I just heard that he said it was because of hair pulling. We’re not women, we’re playing football.
“If you’re giving that as a red card, you can be sent off for any foul. One hundred per cent, that is not a red card.”