"Chelsea are tough, well organised opponents. The biggest danger is that they take the lead because it is very hard to come back against them," Gudjohnsen told a news conference on Monday.

"We have to be focused at all moments because they will make the most of the slightest lapse."

The Iceland international spent six years at Chelsea before being sold to the European champions in June for 12 million euros ($15.01 million) but does not feel under pressure to perform against his former employers.

With Cameroon striker Samuel Eto'o out injured Gudjohnsen is likely to lead the line for Barca. He has scored two league goals so far this season.

"I know what I am capable of achieving, as do the people at Chelsea because I played more than 250 games for them," Gudjohnsen said.

"It's a game I'm really looking forward to and I don't think I have to prove anything to anyone except myself."

When asked why he thought the English champions may have been struggling a little this season he responded jokingly: "Because they have lost their best player."

Chelsea top Group A with six points from two games, two ahead of Barcelona who drew 1-1 away to Werder Bremen last time out.

Barca host Chelsea in the return in the Nou Camp on Oct 31.