Mertesacker insists Arsenal locker room behind Szczesny
"It's his first game after a bad injury so he needs time but he's very important for us," he told talkSPORT.
"We didn't concede a goal this season in three matches so we wanted to stay like this all the time.
"It was disappointing but everyone makes mistakes. We're a team and we have to stick together especially in such moments.
"Our goalkeeper is important for us, especially in the next few matches. We're happy to have him here. That wasn't our first thought, but our second.
"We have to keep our chins up, especially him."