Glenn Roeder revealed he was surprised to see how much power the 26-year-old Frenchman had lost during his spell with Rangers.
Roeder: "The one thing that shocked me when I saw him - I tried to sign him when I was at West Ham and he was quite a thick-set, chunky lad, but the regime at Rangers made him lose an awful lot of weight.
"I think he has lost strength because of that. It has affected him physically in terms of his power. He has lost an amount power.
"But we will get that back. We will build him back up to be the shape of the Olivier Bernard we remember, not this slim, thin one that we have now.
"You can become too thin and lose your power and strength. There are a number of players, if you go back through the years, who were outstanding players even though they looked, if you want, a little bit chunky."