The injury is not as serious as those sustained by Craig Beattie and Maciej Zurawski but the 26-year-old is likely to miss this weekend‘s Tennent‘s Scottish Cup tie against Clyde, as well as SPL matches against Kilmarnock and Motherwell.

His enforced absence could provide a short-term solution to the problem of making room for Roy Keane in a team who have been performing well in recent weeks.

However, Stephen Pearson, who replaced Petrov and launched Celtic‘s comeback in the 3-2 victory against Hearts, has also given manager Gordon Strachan plenty to think about over the coming weeks.

Speaking to the club‘s official website, www.celticfc.net, Strachan said: “Stan’s injury is not as severe as Beattie’s or Zurawski’s but it’s to the same area.

“If you’re asking for a timeframe, although it’s difficult to say at the moment, I’d say we’re probably looking at him being out for about three weeks.”

Strachan believes Petrov‘s performances were suffering as a result of a gruelling schedule for club and country, which recently included a trip to the United States with the Bulgarian national team to take part in friendlies.

And the Celtic boss hopes the enforced rest will prove to be a blessing in disguise for the talented midfielder.

He added: “It’s never good losing a player like Stan, but hopefully the rest will do him good.

“I think it’s probably fair to say that he hasn’t been as dynamic for us over recent games and, if you look at his performances, I think there’s a lot there to suggest that his body has been getting tired.

“When you look at the games he’s played, it’s no real surprise.

“He’s not missed many matches for club or country over the last couple of years and, when you look back to those games he travelled to America for recently with Bulgaria, maybe it’s just all beginning to catch up with him now.”