Chelsea defender Branislav Ivanovic admits his side have only themselves to blame for their spluttering form as they bid to avoid an FA Cup embarrassment in Sunday's fourth round replay against Brentford.

Rafael Benitez's team were below their best again in an unconvincing 1-0 win at Sparta Prague in the Europa League on Thursday and the lacklustre display only added to the impression that the Blues are painfully out of sorts.

Fernando Torres took the brunt of the criticism after missing two golden chances to open the scoring but, while the Spanish striker can have few complaints after scoring one goal in his last 13 appearances, he isn't the only one to look short of motivation and inspiration in recent weeks.

With League One minnows Brentford desperate to inflict more misery on their west London neighbours, Chelsea can't afford to underestimate a team that came close to a shock win in the 2-2 draw at Griffin Park last month.

Serbia international Ivanovic acknowledges that Chelsea's lack of consistency over the course of the campaign is a worrying trend which must be addressed.

"We go up and down this season," he said. "We have to look at ourselves and our performance.

"We have had a lot of games. We have played every three days for the last four months. This has made it difficult. Sometimes you're not recovered and don't have a big enough squad.

"All these things affect results, but you have to be stronger. Now we have some time, we can recover and play our games with a better performance."

Benitez and Torres were again subject to the fans' ire throughout the win in Prague and Chelsea could do with a morale-boosting Cup run to lift the gloom around Stamford Bridge.

The Blues, who would face Middlesbrough in the fifth round, have often bounced back from poor starts to finish the season strongly, including last term when they won the FA Cup and Champions League under Roberto Di Matteo.

But it took a Torres equaliser to spare Chelsea's blushes against Brentford in the first meeting between the two clubs for 63 years.

And Ivanovic, who made his 200th appearance for Chelsea in midweek, knows Benitez's side badly need to go on a long winning run to restore belief.

He hopes the result in Prague and a victory over Brentford at the Bridge will provide the springboard to do exactly that.

"It was a very important game for us to win and to keep the momentum going," Ivanovic said.

"The lack of consistency has been very difficult for us, but we are a team that can build and we have to think about this.

"We have to improve every game, every session and we hope it will be fine in the end."

Chelsea will be boosted by the availability of key players against Brentford, with David Luiz back from suspension, Demba Ba available after being ineligible in Europe and Victor Moses and John Obi Mikel fresh after being rested following their Africa Cup of Nations win with Nigeria.

John Terry, who has been struggling with a knee injury, could also play after being an unused substitute in the Czech Republic.

Meanwhile, Brentford boss Uwe Rosler does not believe his side blew their only chance to beat the FA Cup holders when they allowed Torres to equalise.

"Obviously Chelsea will take us more seriously than the first game and I am looking forward to what will be a great test for us, for everybody involved," Rosler said.

"I still believe it is possible. The chances are slimmer but I think it is still possible.

"We need to keep it at 0-0 in the first half an hour, keep our options open and also be brave to attack them."