The Germany international, the Gunners’ record £43million signing last year, hit the ground running in north London and began the season with a flurry of assists and goals.
However, that form has tailed off significantly following some seemingly lacklustre displays, highlighted by his penalty miss in the 2-0 Champions League defeat to Bayern Munich on Wednesday.
However, Mertesacker believes too much is expected of his compatriot, especially in what is only his first term with the club.
“We have a lot of games here in England and everyone is tired, but it is not just up to Mesut,” said Mertesacker ahead of Saturday’s Premier League clash against Sunderland.
“It is up to everybody to encourage and come back, during the game we all need to encourage each other.
“Mesut has played a lot of games and he is a massive player, we need him at his best. Game by game, he will come back stronger.
“It is not normal to come here and perform well in the first season over 50 games.
“Mesut is very important for us and he is a very creative guy. We need his assists and his goals, so the best is to encourage him.”