Michael Owen could miss England's crucial Euro 2008 qualifiers against Estonia and Russia next month after it emerged on Monday night that the striker will have to undergo a hernia operation at some point.

Owen was substituted after 55 minutes in Newcastle's 1-0 defeat to Derby County and Toon boss Sam Allardyce admitted that the 27-year-old was feeling " tightness" in his groin.

However, The Independent understands that Owen's problem is more serious than that and an operation will be needed on his groin at some stage.

The timing of that surgery will be crucial to England's Euro 2008 qualification campaign. Hernia operations ordinarily require around three to four weeks recuperation before a player can get back to action. England play Estonia on 13 October and face Russia in Moscow on the artificial pitch at the Luzhniki stadium four days' later.

Allardyce played down the extent of the striker's discomfort yesterday saying that his substitution was "precautionary". But he did concede that the club were not certain that Owen would be fit to play against West Ham on Sunday.

"He wanted to carry on but he felt his groin at half-time," Allardyce said. "I just didn't want to take any risks. I let him go out [for the second half] but didn't think he looked very comfortable so I put Oba [Martins] on pretty quick.

"I just hope Michael's [injury is] not too serious. We don't think it will be, you can expect a little tightness with all the games he's had and particularly the two England games and, of course, he hasn't had that many over the last couple of years so he's getting better and sharper and fitter. He felt the groin [last night] and had he carried on and extended himself in any way, he might have actually pulled it. We don't think he has, we think he's going to be OK for Sunday against West Ham."