The Leicester City midfielder suffered a serious knee injury early on in the win over Southampton.
Leicester City manager Nigel Pearson has admitted that the knee injury Matty James suffered against Southampton was a bad one, telling the press conference ahead of the trip to Sunderland that the midfielder could be out until 2016.
The 23-year-old has ruptured his anterior ligaments, and will be out between six and nine months.
“It’s disappointing for Matty," admitted Pearson, as quoted by the club website. "He has been among our most consistent performers in the last three seasons and is an enormously popular member of the squad. We all wish him a speedy recovery.
“Recovering from long-term injury is as much of a mental challenge as it is a physical one and, if the positive attitude Matty has shown this week is anything to go by, we can expect him to come back as strong as ever.
“He has a fantastic work ethic and is a strong character, which will be important for him in the coming months.”
The former Manchester United youngster has been a key man since he and Ritchie de Laet moved to the King Power stadium in 2012.
James played 40 times last season as the Foxes won the Championship, and has been a regular fixture in Pearson's side this year, having made 27 league appearances and playing his part in the recent excellent run that has seen Leicester move out of the relegation zone.
His long-term absence will be a bitter blow for the side, but may open the door for another former United player in Danny Drinkwater. The 25-year-old has seen his playing time reduced since the club were promoted to the Premier League, and he replaced his former Old Trafford teammate during the win over Southampton.
Having been on the bench for much of the second half of the season, Pearson will not only hope that James is available as soon as possible, but that the likes of Drinkwater will seize the opportunity the injured midfielder's absence has presented.