In other circumstances, there might have been rueful talk about the curse of the Player of the Month award, which Wayne Rooney was proudly parading an hour before damaging ankle ligaments while training yesterday. But the latest interruption to the Manchester United forward’s career is likely to increase concern at Old Trafford about his apparent susceptibility to injury.

The expected four-week layoff represents another untimely blow to Rooney, who has been in magnificent form in recent weeks since returning from the third metatarsal fracture of his young career.

That injury, on the opening day of the season, led Sir Alex Ferguson to instruct Rob Swire, the physiotherapist, and the club’s sports science department to investigate the cause of the metatarsal fractures, with the United manager hinting that Rooney’s running style – “he’s very powerful and comes down heavily on the ground” - may be a factor. Even if yesterday’s setback owed more to bad luck, with the 22-year-old said simply to have “gone over” on his right ankle, the last thing that United wanted was another injury to investigate.

After scoring nine goals in as many outings for club and country since October 2, Rooney had been backed by Ferguson yesterday morning to beat a personal best of 23 goals at club level this season, but a couple of hours later the player was hobbling off the pitch at United’s Carrington training complex after falling awkwardly. The immediate prognosis from United’s medical department was that he will not play for four weeks.

With United through to the last 16 of the Champions League and an international break looming after tomorrow’s Barclays Premier League match at home to Blackburn Rovers, the greater loss on this occasion may be to England. But Rooney’s latest injury will cause much frustration at Old Trafford, where he and Carlos Tévez have enjoyed a flourishing strike partnership in recent weeks, helping United to score 22 goals in their past six matches.

Their form was such that Ferguson indicated yesterday morning that Louis Saha, who is fit again after a succession of injury problems, may have to content himself with a role as an impact substitute for the foreseeable future. “I think Louis makes a bigger impact as a substitute,” the United manager said.

The injury to Rooney, though, is likely to change that, with Saha in line to start a league match for the first time since February 10. Facing Saha, rather than Rooney, would ask different questions of Blackburn, but Mark Hughes’s team have been in superb form in recent weeks, and the manager’s feats have strengthened his position among the favourites to succeed Ferguson when the 65-year-old retires as United manager, a job that Hughes would fancy.

“Certainly, compared to when Alex first arrived, United is now a huge operation and the fact he can give more jobs to people that he trusts has possibly made the job easier,” Hughes said. “But the manager still has to pick the right team to win football matches and he has continued to do that for 21 years.

“I could never say that he will turn around and call it a day if he won another Champions League. He has earned the right to make the decision whenever he wants.”

United last night beat Liverpool to the signature of John Cofie, the 14-year-old forward who is rated as one of the outstanding young prospects in English football. Cofie has been affiliated to Burnley’s school of excellence and was expected to move to Liverpool’s youth academy. Coincidentally, one of Burnley’s most famous supporters, Alastair Campbell, Tony Blair’s former director of communications and strategy, attended Ferguson’s weekly press briefing yesterday.