Owen Hargreaves faces a battle to save his career after suffering a fresh injury setback, Manchester United's manager Alex Ferguson revealed today.

The midfielder, who has been blighted by severe knee injuries over the past two years, will miss the start of the season having made just one appearance last term – as a 92nd minute substitute in United's penultimate league game.

The 29-year-old had hoped to get his career back on track having returned to pre-season training ahead of United's tour to North America. However, Ferguson now admits he has no idea when Hargreaves, who has made just 38 appearances for United since his £19m move from Bayern Munich three years ago, will be back.

Ferguson told MUTV: "The bad news is that Owen Hargreaves is back in America seeing the specialist. He won't be ready for the start of the season. I don't know when he'll be back."

Richard Steadman, the Colorado-based surgeon who operated on Hargreaves, told him that his knees were in a worse state than those of any professional footballer he had examined in 35 years. Asked if he feared being forced into retirement, Hargreaves said recently: "It is only human to think that way. The longest injury before this was when I broke my leg at Bayern Munich and I was out for a couple of months.

"Football is a physical game and injuries are part of it. But I could never imagine having one that has impacted on me so much. I thought – everyone thought – I would be fit for the start of the season. It didn't materialise.

"It has been a pretty humbling experience and I am sure many people doubted me but anybody who knows me knows that what I set my mind to I get."

The Canada-born player will now miss United's pre-season tour, which commences with a game against Celtic in Toronto next Friday, and Ferguson also confirmed that Michael Owen is unlikely to make the trip.

However, there was better news for some of United's other injured players. "Antonio Valencia should be OK and Nani should be ready for the start of the season, too," Ferguson added.

"Michael Owen is doing great – he's doing all his work in the gymnasium every day. I don't think he'll be fit to go to America but he should be ready for the start of the season."