Arsenal hero Martin Keown has concerns with Alex Song going into the back four for their Champions League tie with Olympiakos.
In his column for the Daily Mail, Keown wrote: "If you had to pick one of the Arsenal midfielders to move back into defence, it would be Alex Song.
"He is strong and brave and has done it before, most notably against Barcelona in the Champions League a couple of seasons ago. Per Mertesacker will have to look after him and marshal him through the game.
"Arsene Wenger clearly feels Song has the attributes to play at centre half but he would agree that it is not ideal.
"I worry about whether he is explosively quick enough to deal with the change of pace some strikers will have."