Brentford secured a 2-2 draw on Sunday with the Blues twice going behind at Griffin Park and needing goals from Oscar and Fernando Torres to snatch a replay at Stamford Bridge.
After the result Bees boss Rosler underlined the pressure faced by the Blues, who have already been knocked out of the Champions League and Capital One Cup.
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"When we do our job I think we can again make it difficult. Of course, we have no pressure. We have everything to win and nothing to lose. We have won already today a lot by earning that replay.
"Chelsea Football Club has to win titles, but they are not in the Premier League or Champions League any more and they had to put a lot of effort into this game."
The former Manchester City striker also pointed out the strength of the Blues’ line-up on Sunday, with goalkeeper Ross Turnbull the only player rotated into the side in place of the rested Petr Cech, while John Terry returned from injury and Juan Mata was introduced at the break with his side a goal down.
The former Manchester City striker added: "I felt when you saw their starting line-up that they didn’t rest any of their big players.
"They had a very strong team out there, that said they realised they had to bring a strong team out here at Griffin Park to give them a strong chance to win the competition."