SAM Allardyce is keeping his fingers crossed that Gary Speed can overcome the back problem that threatens to rob Wanderers of their most effective midfield dynamo.

Veteran Speed was playing a key role in frustrating Chelsea at Stamford Bridge on Saturday before being forced to withdraw at half time.

He was sorely missed as Wanderers, leading 1-0 and knocking Jose Mourinho's men out of their championship stride, were over-run and eventually overwhelmed, going down 5-1 their heaviest defeat for two years.

Allardyce, already without Ivan Campo, Nicky Hunt and Jay Jay Okocha, is worried that his squad is being stretched to its limits at a time when fixtures are piling up on the domestic and European fronts.

But it was the loss of Speed, whose back condition is giving him hamstring pain, that caused him most concern on Saturday and leaves him struggling for Thursday's UEFA Cup tie in Besiktas and possibly longer.

Allardyce was riled by Rob Styles' decision not to send off Chelsea midfielder, Michael Essien, for what he described as a "career threatening" challenge on Tal Ben Haim in the first half. But he considered Speed's absence in the second half was the more decisive factor.

"Losing Gary Speed was a major blow for us," he said. "It was going to be hard enough for us to hang on at 1-0 with him, but without him we lost that extra defensive quality we needed in midfield.

"I certainly don't think we would have gone down as heavily as we did, if he'd stayed on.

"But because we had to replace him (Hidetoshi Nakata took over) we couldn't hold on for that 10 to 15 minutes at the start of the second half that would have been vital.

"I also don't think Ricardo Gardner would have got himself in a position to get sent off if Gary had been in there."

Wanderers were already 2-1 down when Gardner was red-carded for deliberate handball in the 59th minute. Frank Lampard scored directly from the free kick to stretch Chelsea's lead and put Mourinho on his way to his biggest victory in English football.

Allardyce sympathised with his players for not getting the rub of the green at crucial stages, although he was critical of certain aspects of their play, blaming Jussi Jaaskelainen for Chelsea's first, when he parried Lampard's free kick straight into Didier Drogba's path, and was annoyed that the defensive wall did not do its job when Lampard netted the third.

"It wasn't so much great finishing by them but poor defending by us because Jussi should have done better for the first one and the wall wasn't positioned right for the free kick Lampard scored," he said.

"Once they scored their first they got the momentum and we really laid down a little bit. They got 2-1 up and once Ricardo was sent off they were in full flow.

"I'm not taking anything away from Chelsea but, unfortunately for us, when we needed a bit of luck, it went against us.

Allardyce, meanwhile, has warned his fellow Premiership managers they will have to pull a rabbit out of the hat, if they are to deny Jose Mourinho a second successive Championship crown.

Chelsea are nine points clear of the field after only nine games 10 points clear of Manchester United and 14 ahead of Arsenal - and the Bolton boss believes the Stamford Bridge men will take some catching.

"I'm sure he (Mourinho) is wise enough and his players are wise enough to know it's far from over," he said.

"Many times before teams have come from the back of the pack, but are the teams at the back good enough?

"You're already looking at Chelsea having to have a major slip-up and somebody like Manchester United or Arsenal or Newcastle winning probably 15 out of 16 games and hoping Chelsea lose five, when they only lost one all last year.

"You'd like to see somebody trying to catch them, but Chelsea have got to take every credit for what they've done."