Juventus defender Dani Alves suffered a broken leg in Sunday's 3-1 defeat to Genoa, the Italian champions confirmed.
The Brazilian was stretchered off following a collision with a little over 10 minutes remaining, leaving Juventus with 10 men after they had already made three substitutions.
Juventus announced after the game that initial tests showed that Alves had a fracture in his left fibula, the smaller bone in his lower leg, and he will be evaluated further on Monday.
Fellow defender Leonardo Bonucci also injured a thigh muscle in the defeat, and Juventus said the extent of the damage would be determined after more tests.
The injuries leave Juventus thin at the back with Andrea Barzagli already out until the new year after dislocating his shoulder, while Giorgio Chiellini has struggled to stay fit.
Juventus manager Massimiliano Allegri was not pleased with Genoa's tackles, but he criticised his "lightweight" side for falling behind by three goals inside 30 minutes.
"There were 25 Genoa fouls and only eight from us," he told Sky Sport Italia. "When those are the stats, it is impossible to win a game of football.
"We knew Genoa were tough and that we would have to play on their level physically, but the first half was really bad. The second was better, but by then it was too late.
"It's a setback. I presume it's because of a dip in concentration levels after qualifying for the Champions League [knockout phase].
"We conceded three goals from inside the six-yard box. Again, you're always going to lose a match if you do that.
"In every season there is a slip-up and this was ours, because we were just absent in the first 30 minutes. There are no excuses for that start.
"We were too lightweight. We still have a four-point advantage in the table, fortunately, but this match requires us to really sit down and think about things. It has to make us reflect and learn valuable lessons."
Ivan Juric, meanwhile, had nothing but praise for his Genoa players.
"Today every single one of the lads played at an extremely high level," he said. "We are really happy that we've managed to beat Juventus in this fashion. Now we want to secure our position in this league and keep on improving."