Can't remember exactly where I have read this, but here goes.
The gist of it was that Paul Le Guen is a fitness freak and made Olly and a few other players lose a bit of weight, resulting in him losing muscle and strength.
Remember roeder saying that a lot of Bernard's game is based on his strength, so will take him few weeks to get back to full match fitness and strength.
This was about 2 weeks ago by the way.