Villa have been dealt a huge injury blow after captain Stiliyan Petrov was effectively ruled out until 2011.

The midfielder was forced off with a knee problem in Saturday’s 1-0 defeat to Sunderland at the Stadium of Light and scans over the weekend have seen manager Gerard Houllier’s worst fears realised.

Petrov is expected to be sidelined for a minimum of two months, leaving him a major doubt for the entire Christmas period.

Boss Houllier, speaking at the club’s opening training session at Villa Park, said this afternoon: “Unfortunately Stiliyan Petrov will be out for two months, if not more.

“It’s a bad one – a partial tear of the medial ligament. It takes time to heal.

“We will find out in the middle of the week whether it requires an operation or not.

“It’s a grade three type injury so it might need a minimum of two months.

“When he made a tackle a player fell on his leg and it twisted his knee.”

Petrov’s injury comes as a further blow to Villa, who are already facing up to being without full-back Luke Young and possibly Gabby Agbonlahor for Sunday’s Second City derby at home to Birmingham, with hamstring and groin injuries respectively.

Steve Sidwell, who replaced Petrov against the Black Cats, would be the obvious candidate to step in for the captain.

Looking back on Saturday’s game, Houllier insisted Villa should have had a penalty when Nigel Reo-Coker was brought down by a combination of Titus Bramble and Lee Cattermole early on in the contest.

He said: “That is the only claim I have. But the referee decided otherwise.

“There is no point arguing, it will not change the result.”

Houllier also reckons his players need to show more belief.

He said: “Maybe because we are changing a few things like the philosophy of play it will take time.

“We know where we are going but sometimes it looks as if they can do very well and they don’t believe in that.

“The team have had practically three managers in a month and a half – you have got to take that into account.

“Some players thought they would never play then they have come back into the picture, others don’t play as regularly so it is an unsettling period for a team.”