By Chris Harris

Arsène Wenger believes it is "far from impossible" for Chelsea to knock Barcelona out of the Champions League this week.

Roberto di Matteo's side withstood a wave of pressure in the first leg of their semi-final tie at Stamford Bridge last Wednesday and grabbed a winner on the counter-attack through Didier Drogba.

Barcelona's cloak of invincibility slipped once again on Saturday when they lost at home to Real Madrid to effectively surrender the Spanish league title. And Wenger believes Chelsea can succeed when Arsenal narrowly failed last year.

"We have some regrets because we lost on the backheel of Fabregas in the 45th minute, and we got Van Persie sent off at 1-1. So it's far from impossible to qualify there because Chelsea go there in an even better position than us - they won 1-0 and 1-0 is a fantastic result.

"It is far from impossible and, as well, Barcelona, as we have seen the other night, are not the Barcelona of last year. I believe Chelsea could rest eight players on Saturday but Barcelona could not afford to rest anybody [for El Clasico]."

Lionel Messi is the obvious threat to Chelsea but the world's best player will be playing his third match in six days on Tuesday night - and Wenger believes he is feeling the effects.

"At the moment Messi looks a bit tired," he said. "He is still dangerous when he's tired but Chelsea managed to block a few shots from him on Wednesday night but usually he has such a short back lift that it is very difficult to do that.

"It means he is not as sharp as he was before. So if Chelsea defend like they have done the other night they have a chance."

Defence will be Chelsea's first priority at the Nou Camp but Wenger believes they must also pursue an away goal if at all possible.

"In a European Cup game you can understand [Chelsea being defensive] because even if they decided to play otherwise, they would not have much choice because Barcelona have 70 per cent of the ball," he said

"But you wonder as well if it's not worth trying to score a goal because that would mentally be a massive blow to Barcelona. I saw that last year when we scored, it was a lucky goal but I could see suddenly they became very nervous."

Copyright 2014 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source 22 Apr 2012