Arsenal goalkeeper Wojciech Szczesny has no doubts Per Mertesacker will prove his worth in the Premier League.

The Pole has made a point of analysing the performances of ­under-fire Germany star Mertesacker.

Szczesny said: "Per has been very good. You don't pay £10million for a centre-back who is no good.

"Everyone needs time to ­adjust to English football and Per is an experienced player. He's looked very good and is getting better and better."