Aston Villa manager David O'Leary's preparations for tomorrow's Premiership match at home to Middlesbrough have been thrown into disarray after Juan Pablo Angel injured his ankle in training yesterday.

O'Leary fears Angel will be out for around three weeks - meaning he would miss the derby at Birmingham City on March 20 - after the Colombian striker fell awkwardly and his ankle became badly swollen.

O'Leary, who confirmed on-loan forward Carlton Cole has returned to Chelsea for treatment on his injured knee, must now pair together Darius Vassell and rookie striker Luke Moore in attack against Boro.

And the Villa boss knows that is asking a lot of Vassell, who only returned to firstteam duty last weekend as a substitute against Everton after four months out with a broken ankle.

"Juan twisted his ankle in training," said O'Leary last night. "It is very swollen and far too early to tell what the full extent of the damage is.

"The problem is that we can't scan it until the swelling has gone down, but my guess is he will be out for at least two or three weeks. It doesn't leave me with much up-front so Darius will start as, apart from Luke Moore, he is the only fit striker I have got available to me."

O'Leary would have preferred to ease Vassell gently back into first-team action, but with ten games left and Villa's season hanging in the balance, the Irishman needs the striker to find his form immediately.

Consequently, O'Leary has challenged the mercurial 24-year-old to repeat the impressive displays he has shown in recent years for England in the claret-and-blue of his club colours.

And O'Leary says Vassell will have to do well for Villa if he has any hopes of regaining his place in the national setup as there are several English forwards performing well.

He added: "I think Darius really needs to show everyone at Villa that he's capable of reproducing for us over 90 minutes what he does for England in half-an-hour from the bench.

"That's the challenge for him now. We have had glimpses of his talent but we need to see it on a regular basis.

"I can understand why Wayne Rooney, Alan Smith and Jermain Defoe might be ahead of him now in Sven-G^ran Eriksson's mind.

"Darius has a battle on to get his place back in the squad but the only way he can do that is by playing well for Villa over 90 minutes.

"That's the Darius Vassell the past three managers at Villa have been looking for and what I want to see."

While Villa are hopeful Vassell will play a prominent role in their remaining fixtures, on-loan Cole has returned to Stamford Bridge for treatment to his knee injury.

The striker sustained cartilage damage in a recent England Under-21 game and had feared he needed surgery to overcome the problem.

Chelsea believe a period of rehabilitation will cure the trouble but O'Leary says it is "touch and go" whether Cole will return to Villa before the end of the campaign.

He said: "Our doctors wanted to do things a certain way, but we sent him down to Chelsea and they wanted to do things a different way.

"He's their player, so they've kept him down there to do it their way. I'd say it's touch and go whether we'll see him again this season. It's just whether he responds to the treatment.

"I wouldn't rule him out. He could get the last couple of games in at the back-end of the season."

With Mark Delaney still not fit to return from a knee injury, O'Leary's injury problems are mounting up but the

beleaguered Villa boss has at least been cheered by midfielder Gavin McCann's improvement.

McCann has been sidelined since undergoing knee surgery in January and it was thought he would not play again this term but McCann is jogging again and could be back before the end of the season. n Villa's 18-year-old striker Gabriel Agbonlahor signed a new contract yesterday committing him to the club until June 2007.

A regular in Kevin MacDonald's reserve-team squads this season, Agbonlahor broke Vassell's youth scoring record last term, scoring an amazing 40 goals.