Berbatov was not named in the squad as Manchester United drew 1-1 at Birmingham in the Premier League on Saturday evening, and Ferguson has now revealed the striker could face a spell on the sidelines as they seek to resolve his knee concerns
"Dimitar wanted to play with it but we felt we should try to get it (the knee) sorted and get him fit again," Ferguson said. "He may have to have an exploratory operation."
In Berbatov's absence, Mame Biram Diouf made his debut for the club as an 81st minute substitute but, with Darren Fletcher having been dismissed three minutes later, Ferguson admits it was difficult for the 22-year-old as Wayne Rooney dropped back into midfield.
"I'd hoped to put Diouf up front with Wayne," he said. "We know he can play alongside someone but to play on his own in his first game was difficult for him."