The on-loan Finland international striker has been struggling for most of the season with the injury and it was decided by Blues, Chelsea and the player for him to rehabilitate with the London club.
Forssell has had the imflammation drained out of the knee and is expected back in training with the rest of the Blues squad at Wast Hills at the end of this week and could well return to the squad for the game against Bolton at The Reebok on Saturday evening.