Leonardo Bonucci has suffered an ankle injury, Serie A champions Juventus have confirmed.
The defender started Sunday's 2-1 win at Lazio but had to be replaced before half-time, having tried to play on after being hurt early in the game.
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Juve announced in a medical update on Monday that Bonucci has sprained his right ankle and reports have claimed he could be out of action for as long as a month.
The Italy international has already begun treatment for the injury, but is now a doubt for the first leg of Juve's last-16 Champions League tie with Atletico Madrid on February 20. The second leg will be held in Turin on March 12.
Bonucci has quickly become one of Juve's key players again, starting 17 games in Serie A this term, since his return from a brief but underwhelming spell with AC Milan.
He is the latest addition to the list of stars on Juve's injury list, which already includes fellow defender Andrea Barzagli, as well as Mario Mandzukic, Juan Cuadrado and Miralem Pjanic.
"In times of difficulty this team and this club has always been able to respond in an excellent way," Bonucci told Sky Sport Italia last week when asked about their growing fitness issues ahead of Sunday's game against Lazio.
"We can do it again. Barzagli, [Joao] Cancelo and Pjanic are important elements for us, but we are not looking for an excuse."
Coach Massimiliano Allegri confirmed at the weekend that Medhi Benatia looks set to leave the club, but they will add another defender to their ranks as Martin Caceres is on the verge of returning for a third spell in Turin.
"It wouldn't make sense to keep a player who is reluctant," Allegri said. "Benatia made a choice and the club evaluated and accepted his request.
"I know Caceres and he can give a lot to Juventus. He is a player who is ready to go here, while others would take more time settling in, learning the environment."
Juve's win at Lazio, sealed by a late Cristiano Ronaldo penalty, saw them move 11 points clear of Napoli at the top of the table as Allegri's men seek to clinch an eighth consecutive title.