Arsenal defender Per Mertesacker is ready to face Chelsea striker Demba Ba today.

He will today come face-to-face with an old foe from the Bundesliga in Ba.

Mertesacker said: "I have played against him in the Bundesliga. He did well at Hoffenheim.

"He is very compact, physically strong and quick. He is always a threat. We must not focus on one player, though. We must take care of our defensive level."