Lehmann, 37, has been carrying the knock since the start of the season but the injury intensified after the clash at Wembley, meaning Manuel Almunia will deputise against Manchester City on Saturday.

The veteran stopper has made errors in his two games this season and was beaten by Frank Lampard at his near post last night, although he also denied Michael Owen with a reflex stop.

Despite his blunders against Fulham and Blackburn, effectively costing Arsenal two points, boss Wenger has total faith in his goalkeeper.

"Apart from the mistakes, he's had good games," said the Frenchman. "You have to defend your goalkeeper and your players.

"You don't judge it on how many mistakes they make - you have confidence in your goalkeeper.

"The problem when you get older is people say you're in decline, but I am still convinced Jens is top drawer."

Wenger confirmed, though, that the Germany stopper is out of the City clash at Emirates Stadium.

"Lehmann will not play, he is out with an Achilles problem that he had already," he said.

"Two weeks ago it became worse and today it was worse still."

It was a bad week for north London goalkeepers, with Tottenham stopper Paul Robinson taking the blame for Germany's equaliser at Wembley.

Wenger, however, defended Robinson, adding: "For the goal, he was calculating on the cross and it is like what happened to David Seaman on Ronaldinho's free-kick.

"If he hadn't come for the cross you say 'what is he doing on his goal-line' and he was unlucky that the ball headed towards the top corner.

"For me, it is not a massive mistake because I like the guy who likes to step out on the cross. I don't like the guy who stays on the line and says 'I make no mistakes'.

"I prefer to be caught once like that and be caught once out of 100, rather than playing completely safe on the line."

Wenger brought goalkeeper Lukasz Fabianski to the club this summer so has plenty of back-up, and he also backed Almunia to seize his chance in the absence of Lehmann.

"Almunia is equipped to take responsibility because he did very, very well when he played last year," said Wenger, speaking at the launch of Arsenal's partnership with the TreeHouse National Centre for Autism Education, the club's charity of choice this season.

"It was very reassuring.

"He is mature, he has all the attributes you need to be successful. It was a close decision who is my number-one keeper because of his performances last season."