Arsenal No. 1 Wojciech Szczesny has been ruled out of his side's opening Champions League game against Montpellier on Tuesday, due to an ankle injury.
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Szczesny, 22, only made his first appearance of the season in the 6-1 win against Southampton on Saturday, after a rib injury kept him out of Arsenal's opening three games of the season.
Vito Mannone is likely to deputise after impressing during the Poland international's absence, while James Shea will be on the bench. Szczesny was considered at fault for Southampton's goal on Saturday, which brought an end to Arsenal's run of clean sheets.
But manager Arsene Wenger has every confidence Mannone holds the "mental strength'' to put his Champions League nightmare behind him - his last European performance for the Gunners saw him produce a calamitous display in the defeat at Olympiacos last December.
"Vito is very close (to the Arsenal number one jersey), and he gets another opportunity now,'' said Wenger. "He has belief and he has the mental strength to deal with that.''
With Lukasz Fabianski also sidelined because of injury, and Argentina youth international Damian Martinez not on Arsenal's Champions League squad list, 21-year-old Academy product James Shea will take an unexpected place on the bench.
"He was on the list as goalkeeper number five at the beginning of the season and now he is number two. That shows you how quickly football can change,'' said Wenger.
Meanwhile, Abou Diaby, who missed Saturday's game due to a hip problem, was in the 18-man squad which left for Montpellier on Monday, but Russian winger Andrey Arshavin is not included.