Arsenal hero Jens Lehmann can understand fans having doubts over Per Mertesacker.

The towering defender is taking time to settle into the high tempo football of the Premier League after playing in the Bundesliga with Werder Bremen, but ­Lehmann is certain he will adjust.

"I know Per from the time we played together with the German national team," Lehmann told the Sunday Mirror.

"He has nearly 80 caps for Germany but that doesn't guarantee ­anything. The type of pressure in international football is totally different to that at a big club.

"You have to prove yourself every day. Maybe the injuries have not helped him. When I was playing the two centre-backs were always Kolo Toure and Sol Campbell.

"The defence has changed a lot at Arsenal this season.

"But what I know about Per is that, mentally, he is very strong.

"When I spoke to him recently he said how happy he was at the club and with the group of players he is working with. He will be a success - I am sure of that."