Szczesny was left back in London when the rest of the squad travelled out to Munich on Tuesday afternoon, with Wenger revealing the Poland international had been "mentally affected" by the number of games he played this season. Lukasz Fabianski impressed in the 2-0 win at the Allianz Arena and is hoping to retain his place.
Skipper Vermaelen, meanwhile, was left on the bench as Laurent Koscielny - whose late header provided Arsenal's second goal on Wednesday night as they went out on away goals - partnered Per Mertesacker. Wenger said: "They (Vermaelen and Szczesny) are two outstanding players who are part of our squad."
Nacho Monreal was cup-tied in midweek and is set to come back into the defence as left-back Kieran Gibbs will be rested after completing his first 90 minutes since his recovery from a thigh problem.
However, Wenger insisted team selection would always come down to individual form.
He added: "They have played so many games until now. Their position is very important in the squad.
"But every position is up for grabs. You have to face it like that, the last game decides the next one.
"All the players are in the same position. Nobody is guaranteed places in the team.
"Everybody faces the same competition and the players who (have) come in have been on the bench for a long, long time.
"They all have the same problem, the job of being a top-level competitor is to deal with that."