Manchester United captain Nemanja Vidic is out for two months after undergoing injury on his troublesome right knee.

The Serbian defender, who missed six months of last season with an anterior cruciate knee ligament injury suffered against Basel in the Champions League, will spend another spell on the side-lines after complaining of tightness in trhe area.

Vidic missed the trip to Liverpool on Sunday with manager Sir Alex Ferguson claiming the 30 year old was being rested but further investigation has led to further knee surgery.

Nemanja Vidic
Vidic will miss the next two months of the season. Reuters

"Sir Alex, as a precautionary measure, rested Vidic at the weekend, after he complained of tightness in his knee, however, further medical investigation revealed the underlying problem," he said.

"The central defender was operated on this week and will be sidelined for about eight weeks."

This latest injury for Vidic will raise fears over his long-term future in the game, with the same knee which he damaged last season being operated on.

His absence will see him miss the Premier League games with Tottenham Hotspur, Newcastle United, Chelsea and Arsenal among others, as well as the next four Champions League group matches.

With Chris Smalling and Phil Jones still both out injured, Vidic leaves United short at centre-back with Jonny Evans, who played against Liverpool and for much of last season in his absence, the likely candidate to fill in alongside Rio Ferdinand.

Michael Keane and Frederic Vesili may also be required at different stages of the season, with both likely to play a part in club's League Cup campaign.

While United are short at centre-backs, the signing of Alexander Buttner in the summer has given Patrice Evra added competition at left-back, and the Frenchman admits he is feeling the heat.

"My biggest challenge is from myself," said Evra. "I am not being arrogant but I am my biggest challenge. People forget very quickly how I got to become United's left-back.

"There was Gabriel Heinze and Mikael Silvestre. When I hear people say Patrice never had someone to fight him for his place I just say they have to remember I fought with two great left-backs. They have bad memories!

"I will keep fighting, too. It is too easy for people to say that now we have bought another left-back, 'Oh yes Patrice Evra will have to fight for his place now.'

"Patrice Evra has always fought for his place. It doesn't matter if someone is there or if they're not, I will fight because you have to respect the shirt. When you play for Manchester United that is the big challenge."