England could be without striker Michael Owen for very important Euro 2008 qualifiers in October.
Owen had to be substituted in a game for Newcastle United on Sunday and he may need an operation to fix it.
England play Estonia on 13 October and Russia four days later as they try to qualify for the European Championship in 2008 in Austria and Switzerland.
If Owen does need an operation he will be out of action for three to six weeks, so would miss those two matches.
Owen's club boss, Sam Allardyce, said: "I am worried he asked to come off. If Michael needs an operation, he will have it straight away."
Owen got a bad injury at the World Cup in 2006 and missed most of last season because of it.
He has scored five time since returning to action, including three times for England in this month's Euro 2008 qualifying victories over Israel and Russia.