"He has played many games, a lot under pressure," Wenger told the Daily Mail. "He had one or two games when he was performing less, but it is difficult with goalkeepers. Do they find their confidence again when you give them a breather or just keep playing them.
"I decided to give him a breather and time for him to refresh. This is not because of the pressure, but when people talk about you there is a feeling you cannot afford any more errors.
"It is only his second season at the top level. If you look at the number of goalkeepers at the top level, you do not have many of that age. He has played many games and it is difficult to absorb everything that goes with being at a big club."
The North London outfit trail Bayern 3-1 after the first leg at the Emirates Stadium.