The club's record signing, who returned from injury at Hull last week, has found it hard to sustain his early season form but Mertesacker maintains he has what it takes to succeed at the Emirates.
"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."
Meanwhile, manager Arsene Wenger has admitted Abou Diaby, who has been out for over a year, could yet feature before the end of the season.
The midfielder played 45 minutes for the U21s against Chelsea on Tuesday in what was his first action since he suffered a cruciate ligament injury against Swansea 13 months ago.
Wenger said: "He hasn't played for a year, but physically he is ready to play, completely. It is now just decision-making, getting used to challenges again. Everybody counted him out, but he is fit and ready."