Manchester United will be without captain Nemanja Vidic for two months following knee surgery.

The Serbian, who missed the final five months of last season after rupturing his cruciate in the Champions League defeat by Basle, missed Sunday's Premier League win at Liverpool after complaining of tightness in his right knee. However, a subsequent examination revealed a greater problem, prompting Vidic to be sent for an operation, which has now been completed.

An injury on the same knee will be a raise concern for the 31-year-old defender and his manager Sir Alex Ferguson over his long-term fitness. The timing could hardly be worse. United are already without Chris Smalling and Phil Jones leaving Ferguson with only two fit central defenders – Northern Ireland's Jonny Evans and England exile Rio Ferdinand.

Ferdinand has had his own problems with injury over the past two seasons and although the 33-year-old's back problems have troubled him less of late it will still concern Ferguson that he will not be able to rest him at will. Jones, who also has a knee injury, is expected to be ruled out for a similar period to Vidic, while Smalling has not yet recommenced training after breaking his metatarsal.

The defensive problem is not a new phenomenon at Old Trafford. Already this season, Michael Carrick has twice been forced play in that position as an emergency measure. Last Friday Ferguson said he was crossing his fingers Vidic, Evans and Ferdinand remained fit. Those hopes have now been dashed and it remains to be seen who United have to call on ahead of Saturday's Premier League encounter with Tottenham at Old Trafford.

With Ferguson anxious to protect Ferdinand and Evans, it also suggests Michael Keane and Scott Wootton may be in line to face Newcastle in tonight's Capital One Cup third round tie.

Nineteen-year-old Keane has made one substitute appearance for the senior side, whilst Wootton, who went on the summer tour to South Africa and China, is yet to make his debut. England Under-18 international Tyler Blackett could also be involved.

The United manager will at least be buoyed by the return of Darren Fletcher who is expected to start the match. The Scotland midfielder came off the bench against Galatasaray in the Champions League last week – his first appearance for the club since suffering a chronic inflammatory bowel condition last year.

After being placed on an extended break, the 28-year-old twice completed 90 minutes for Manchester United's Under-21 team earlier this month although he is yet to start for the club's first team.

"Darren will certainly play against Newcastle and that is the perfect game for him to start back," said Ferguson. "Then we have the game against Tottenham and he could be involved in that. It depends on how he does on Wednesday.

"It will be his first 90 minutes since 10 months out, so it's a big one for him.

"He is handling the condition at the moment and, as we saw the other night, he is looking fine. It is a matter of hoping the condition stays dormant and he is handling his diet well. Hopefully he gets that break."

United's defensive difficulties

United fixtures in next two months:

Newcastle (Capital One Cup) tonight

Tottenham (League) Saturday

Cluj (Champions League) 2 Oct

Newcastle (League)7 Oct

Stoke (League) 20 Oct

Braga (C League)23 Oct

Chelsea (League) 28 Oct

Arsenal (League) 3 Nov

Braga (C League) 7 Nov

Aston Villa (League) 10 Nov

Norwich (League) 17 Nov

Galatasaray (C League) 20 Nov

QPR (League) 24 Nov

Also on the sidelines:

Chris Smalling (foot)