Birmingham striker Mikael Forssell will be out of action for a month after discovering he needs surgery to cure a hernia problem.
The Finland international has been dogged by injury problems, most notably a knee complaint for the past three seasons.
The former Chelsea player finally looked as if his troubles were behind him after impressing in pre-season and scoring on the opening day of the season at Stamford Bridge.
But Blues boss Steve Bruce admitted Forssell needs to go under the knife sooner rather than later to try and minimise the time he will be sidelined.
Bruce said: 'Mikael will go into hospital on Monday. It looks like he has got a hernia problem and we will do something about it as quickly as we possibly can.
'He will miss the Manchester United and Blackburn games but, with the two-week international break coming up soon, hopefully he will be back available after that. These things usually take three to four weeks.
'You feel sorry for the lad because he has had so many knock backs in recent years but kept persevering. This season, he came back looking sharp and we wondered if he was finally over everything and this will be another blow to him.'
Bruce confirmed that keeper Richard Kingson will be available to face the Red Devils after suffering a bang to the head against Blackburn in the mid-week Carling Cup tie.
He said: 'He's going to be okay. It was a bit of a worry at the time but he is in today and we think he is fine.'