Manchester United striker Dimitar Berbatov underwent knee surgery last week, it has been revealed.

The Sunday Mirror says United's £30million striker went under the surgeon's knife on Monday while his team-mates were preparing to face Wolfsburg in the Champions League.

Berbatov has been struggling since being injured against Blackburn at the start of last month. He missed games against Chelsea and CSKA Moscow before returning to the side.

But the problem flared again when he was on international duty for Bulgaria and he was sent to see a specialist who recommended the surgery.

The operation was a minor procedure designed to "clean out" any floating debris inside his knee.

Berbatov was able to resume light training within 48 hours and he was even fit enough to return to United's bench for the game against Aston Villa yesterday.