Arsenal keeper Jens Lehmann is out for at least two weeks after aggravating an Achilles tendon injury in Germany's 2-1 friendly win over England on Wednesday.
Lehmann suffered the injury against England on Wednesday
Spanish keeper Manuel Almunia will replace Lehman when the Gunners play Manchester City on Saturday.
Arsenal boss Arsene Wenger said: "Jens is out and he will miss two weeks, I think. Maybe more - I don't know.
"He is going to see a specialist in Germany on Friday. He had this injury before but it got much worse."
Wenger is confident that Almunia will not let him down while Lehmann is out.
The problem when you get older is people say you're in decline, but I am still convinced Jens is top drawer
"Almunia is equipped to take responsibility because he did very, very well when he played last year," added Wenger. "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."
Lehmann, 37, has made two high-profile errors for Arsenal in the last fortnight.
He gifted Fulham striker David Healy a goal when trying to deal with a backpass in the Gunners' opening game and let a David Dunn shot slip through his hands to give Blackburn an equaliser on Sunday.
But Wenger says he still has confidence in his veteran shot-stopper.
"Apart from the mistakes, he's had good games," Wenger said. "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."