The Spaniard is expected to play for Arsenal for next fortnight as the German keeper has hurt his Achilles.
Wenger admitted he made a tough decision between the pair at the
start of the season and is confident the 30-year-old can step up.
"Almunia is equipped to take responsibility because he did very, very well when he played last year," said the Frenchman. "It was very reassuring.
"He is mature, he has all the attributes you need to be successful. It was a close decision about who was my No 1 keeper because of his performances last season.
"But Jens had the advantage of experience of having played without disappointing. He had an immaculate pre-season."