Brentford forward Clayton Donaldson has claimed to have witnessed Ashley Cole "getting frustrated" with his Chelsea team-mates during their 2-2 draw in the FA Cup fourth round.
League One side Brentford forced a fourth-round replay with their Premier League opponents as Fernando Torres salvaged a draw with his leveller on 83 minutes at Griffin Park.
The Blues will host Brentford on February 17 at Stamford Bridge, and Donaldson is optimistic of inflicting a shock result, with the side's manager, Rafael Benitez, having struggled for wins at home.
Asked if he had witnessed Chelsea's players becoming agitated on the pitch, Donaldson said in the Guardian: "Absolutely. I was obviously closer to Ashley. He was always mumbling something, always mumbling stuff quietly, but I could still hear what he was saying.
"He was just getting frustrated. He was saying about the forward players not showing, saying things like 'He needs to be there' and pointing. You could just see straight away that he was getting frustrated. That was a good thing.
"We are confident. That [atmosphere at Stamford Bridge] has played a part in their recent form. Obviously the fans are unhappy with the manager - they don't really like him - so any little thing that goes wrong, they're always on their backs.
"I think that has played a part in their recent results so, hopefully, we can put that to our advantage and the take the positives and unrest their fans again at their place."
Donaldson added: "You couldn't really see that they were European champions. We set out to unsettle them, and we did that. They didn't really create that many chances, which I am very surprised about to be honest, especially with the quality of players they have got. That was down to our hard work.
"We'd done our homework on them and we stopped them creating. We have to take some credit for that. We're confident, especially given their run of form at home recently not having been the best. The pressure will be on them again."