Chelsea players are a bunch of p***ies..
On a serious note, as mentioned, injuries play an important role in early retirement, form, player team roles (key, important etc) interaction with him asking him to think about coaching etc after retirement...
I had Giggsy play for another two full seasons from the start of Fm12, no problems!
I had received a PM from a member early this morning about the same thing, it was Drogba if I remember correctly..