Juventus captain Giorgio Chiellini will be out for about six months after undergoing surgery to knee ligaments, the Serie A champions said on Monday.
The 35-year-old international was injured in training last Friday, and newcomer Matisse de Licht replaced him in Juventus's 4-3 win over Napoli on Saturday.
"Giorgio Chiellini underwent surgery to repair the cruciate ligament of the right knee," Juventus said in a statement on their website on Tuesday.
"The expected recovery period is about six months."
Juventus have won their first two league games of the season, seeking their ninth successive title, but will have to play without Chiellini for most of the season.
The Italy defender is likely to return in March, meaning he may be ready to play in the Champions League quarter-finals if Juve reaches this stage of the continental championship.