Anxiety Affected Owen Hargreaves - Sir Alex Ferguson

Sir Alex Ferguson thinks midfielder Owen Hargreaves's failed comeback from chronic knee problems could be partly down to him worrying over a return.

Hargreaves, 29, lasted only six minutes of his first Manchester United start since 2008 before limping off against Wolves clutching his hamstring.

"It is possibly because of a lack of match fitness," United boss Ferguson told Manchester radio station Key 103.

"Maybe a bit of anxiety over his first game had a bit to do with it too."

The England midfielder, who has made only 39 appearances since joining the Red Devils from Bayern Munich in 2007, had played 45 minutes with the reserves and less than 60 seconds of first-team football since his previous game of any significance at Chelsea in September 2008.

Yet, with a significant wave of illness and injury affected the squad, United's medical staff gave Ferguson's £18m signing the all-clear for selection on Saturday.

Hargreaves had barely settled into the match, which United eventually won 2-1 after Ji-Sung Park's late winner, when he pulled up after delivering a cross into the box.

"We took a gamble with Owen," admitted Ferguson. "But he only lasted five minutes.

"It was a disaster. He has hurt his hamstring, which is unbelievable."

No estimate has been given about how long Hargreaves is likely to be out for, but the consequences could be significant for a player who is now in the final year of his contract.

England's best player at the 2006 World Cup finals in Germany has been plagued by knee injuries for two years, undergoing surgery on the problem - performed by famed surgeon Dr Richard Steadman - and seeing numerous attempts at a return hampered by pain and tendonitis.

Hargreaves even sat out United's pre-season tour to America in order to consult specialists in a bid to get to the bottom of the problem, and did not feature in any of the club's first 10 league games before making his fleeting appearance against Wolves.

"He's down in the dumps," United assistant manager Mike Phelan told the BBC on Saturday. "That was a risk, and it didn't work out for us. It's just not happening for the lad.

"We're not sure what the injury is. We'll find that out in the next 24-48 hours."

Meanwhile, Ferguson revealed that captain Nemanja Vidic, Patrice Evra and Paul Scholes had all been suffering from a flu virus, which was partly why he was forced to rely on less experienced players during a patchy United performance.

"We have done really well to get a result," Ferguson continued. "You have to admire the perseverance of the team because we have done it so many times.

"But it was a long struggle because we made so many changes."