Manchester United manager Sir Alex Ferguson has admitted that he continued to play captain Nemanja Vidic knowing he had not fully recovered from a cruciate knee-ligament injury.

Vidic missed six months of last season after picking up a knee problem against FC Basel in the Champions League in December 2011.

The Serbian centre-back returned for United at the start of this season but will miss the next two months of action after undergoing surgery on Monday, and Ferguson admits he knew Vidic had not fully recovered from the original problem.

Sir Alex Ferguson
Ferguson says he rushed Vidic back

"I don't think he was ever 100 percent. I noticed a couple of times in training that he was limping a little bit. Then he started feeling tightness in his knee," Ferguson said.

"He wanted to carry on and in that situation that is what tough guys can do.

"Obviously the main operation was to correct the cruciate but when you do cruciates there is always the danger that the cartilage or meniscus is damaged also and that was the case."

The injury leaves United short at the back, with Rio Ferdinand and Jonny Evans the only recognised fully fit centre-backs, with Vidic joining Phil Jones and Chris Smalling on the sidelines.

With Ashley Young set to be accompanied by Antonio Valencia on the treatment table, the 12-time Premier League champions are suffering an injury crisis at one of the busiest periods of the season.

United youth pair Michael Keane and Scott Wootton played at the centre of defence for the Capital One Cup win over Newcastle United but are unlikely to be used during the Premier League game with Tottenham Hotspur on Saturday.

At the other end of the pitch, Ferguson has an embarrassment of riches, with the return of Wayne Rooney giving the Scot a selection headache ahead of the visit of Spurs.

The game could mark the first start together for Robin van Persie and Rooney since the former's move to Old Trafford, but Ferguson admits he is still to formulate his plans for his front line.

"It is early doors but at the moment I don't know where I am going in the sense of what my best partnership will be," added Ferguson. "Probably the strongest part of the club will be in the striker department. It [van Persie's arrival] should give everyone a push."

"Danny Welbeck is in the same position as Javier in that they are not the first-team choices at the moment. That doesn't mean to say it will stay that way because competition is always healthy and them being the kind of young lads they are, will be desperate to establish themselves."