Inter Milan's Italy international Nicolo Barella will undergo surgery on his right knee, the club confirmed on Sunday.
Barella was forced off a soaked pitch in the final minutes of the first half of Saturday's 3-0 win under heavy rain at Torino.
The 22-year-old midfielder said he "felt the knee go click," with the outfit initially stating he had suffered a sprained knee.
"The results revealed damage to a fragment of cartilage in his kneecap," Inter said in a statement on Sunday.
"Barella will undergo arthroscopic surgery to remove the fragment."
The news is a blow for coach Antonio Conte whose side are challenging for the Serie A title just a point behind champions Juventus.
"He's a warrior, an important player for us," Conte said on Saturday.
The former Cagliari player, who has scored two goals this season including one in the Champions League, could be out for a month, according to reports in Italy.
He will miss next week's key Champions League match against Slavia Prague, and Barcelona at home on December 10.
Barella has also become an important player for the Azzurri as they prepare for Euro 2020.
He has 12 caps since making his debut in October 2018 under manager Roberto Mancini, and scored three goals.