Handed a surprise start in yesterday's 2-1 win over Wolves at Old Trafford, the 29-year-old lasted just five minutes before signalling he could not continue.

Hargreaves was clearly troubled by his left hamstring and made his way dejectedly down the tunnel for treatment after giving way to Bebe.

Ferguson conceded a lack of match practice may have been an issue for a player who has completed just 45 minutes of reserve team football and a first-team outing that lasted less than 60 seconds since his previous game of any significance at Chelsea in September 2008.

However, after United's medical staff had given Hargreaves the all-clear to feature yesterday, the Red Devils chief feels fear may have played a part.

"It is possibly because of a lack of match fitness," Ferguson told Key103.

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

In an ideal world, Ferguson would probably not have pushed Hargreaves into service from the off yesterday, knowing the player's first start since he had surgery on both knees to cure a long-standing tendinitis complaint was going to be significant.

However, a devastating combination of illness and injury within United ranks left Ferguson with little option other than to turn to his £18million recruit from Bayern Munich.

"We had to take a check on the morning of the game," said Ferguson.

"We pulled Ryan (Giggs) into the squad but unfortunately he was just feeling his hamstring a little bit, so he was too big a risk.

"Paul Scholes was not fit enough to start because he wasn't feeling 100% so we looked at the situation with Owen.

"He has been training very well and the doctor thought he was fine to play.

"Unfortunately he only lasted a couple of minutes."

No estimate was offered about how long Hargreaves is likely to be out but the consequences could be significant.

Now in the final year of his contract, it is hard to see Ferguson offering another without some guarantee the World Cup star will be available even though he made an impressive contribution to a campaign that ended with Premier League and European Cup glory in his first season at Old Trafford.

England coach Fabio Capello, who was at Old Trafford yesterday, might have equal reason to lament Hargreaves' premature exit, although John O'Shea is confident his team-mate can overcome this latest shattering blow.

"I feel so sorry for Owen," he said.

"He was looking forward to it so much and we were all excited for him.

"He has worked very hard to get to this point. There will be one or two niggles, that is bound to happen.

"But he will be back, there is no doubt about that."