Cristiano Ronaldo will be placed in quarantine for two weeks after the Juventus star returned to Turin.
The Portuguese attacker spent almost two months in his native Madeira as the coronavirus pandemic struck Italy, forcing the country into lockdown.
Ronaldo was expected back on May 18, when clubs were initially scheduled to return to training.
The Italian government moved that date forward to May 4 after many regions gave permission for training centres to open again, prompting Juventus to recall the foreign players who had left the country as the Covid-19 situation grew worse.
The players coming back will have to undergo two weeks of quarantine upon their arrival in Italy before they can begin training again.
While Ronaldo, 35, and his family were on the way back to Turin, many of his team-mates were being tested for coronavirus at the Juventus Training Centre.
Aaron Ramsey, Federico Bernardeschi, Juan Cuadrado, Carlo Pinsoglio and Merih Demiral, who is recovering from injury, were all examined.
As of Tuesday, training will resume but players will have to work on their own to abide by social distancing rules.
Although all 20 Serie A clubs voted to get the season underway again whenever it is safe to return and are now easing their way back to training, it remains unknown when football will be played again.
Despite the government's decision to lift restrictions on athletes of team sports returning to training, the nation's Sports Minister, Vincenzo Spadafora, said there is "no way" football can return soon.
Although there have been fears that the government could ban some sports for several months, Italian Football Federation (FIGC) president Gabriele Gravina has warned that such a move "would be the death of Italian football", while Lazio sporting director Igli Tare said clubs are willing to wait several months before resuming the season.
"I heard that the order could come from the Minister of Sport this week," he said. "But that would not be within his remit. FIFA, UEFA and FIGC have explained that the leagues must be finished within the calendar year.
"If we don't start the league again in June, we will do it when it's possible."