"It's very important to understand how the differences are between the leagues," Mertesacker told the club's official website.
"I think he came from La Liga and it's quite different to play there. He has adapted well but there is more to come from him, and I think the second season will be much better from him, because he's a fantastic player.
"He has shown some great skills but he needs to be more consistent, and that's what makes the difference at the end."
Arsenal still have plenty to play for as they look to secure a top-four finish and their first trophy in almost a decade in the FA Cup final next month. Mertesacker believes Ozil can play a key part in that quest.
"I think if you realise quick what it needs, if you are intelligent enough, and he's an intelligent footballer, and I think he will sort that problem out," he said.
"It's similar to myself, when I got my injury in the second part of the season, and afterwards I came back even stronger, because then I realised what is at stake.
"And I think for him it's good to get a little rest now, to be ready maybe for the last few games for us, the World Cup, and then another season. With a pre-season ahead of him, there's more to come from him."
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