Blow for United as Scholes is ruled out for three months

Manchester United's injury setbacks continued yesterday when the club announced that Paul Scholes will have a knee operation on Thursday and is expected to be out for three months. United are also awaiting the outcome of a scan Rio Ferdinand underwent after he was forced off 20 minutes from the end of Saturday's win over Middlesbrough.

There are fears Ferdinand may have aggravated the groin problem that sidelined him towards the end of last season. United are hopeful he will be fit enough to play against Arsenal on Saturday, although the problem will have to be addressed at some stage.

Scholes reported knee problems during training in the run-up to the Champions League victory over Dynamo Kiev last Tuesday. The United manager, Sir Alex Ferguson, said on Friday that a first scan had proved inconclusive, but a second examination yesterday has confirmed ligament damage, meaning that the former England midfielder will be out until February. Scholes will miss at least 13 Premier League games, but could be back for the Champions League knockout stages at the end of February.

United's midfield has resembled an accident and emergency department recently, and Scholes joins Michael Carrick, who dislocated an elbow against Roma earlier this month, on the sidelines, although Owen Hargreaves and Darren Fletcher have returned to action after injuries – while in defence, Gary Neville is also expected to return soon. His seven-month lay-off could end on Thursday when he takes the field for a United reserve match.

Scholes had already made an amazing comeback from career-threatening eye surgery to play a major part in last season's title triumph and, while he had only scored once in 12 appearances so far this term, few were discounting him as a massive influence on the current campaign.

The former United defender Jaap Stam has announced his retirement with immediate effect. The 35-year-old, now with Ajax, revealed that he had taken the decision to quit due to a lack of motivation.

"This decision was not taken overnight," said Stam. "A while ago, I told [the Ajax technical director] Martin van Geel and [managing director] Maarten Fontein that I could no longer motivate myself enough." Stam played for United from 1998 to 2001 and won three league titles, the FA Cup and the Champions League, including the treble in 1999.