O'Dea has no contract with Celtic, it was ended when he went to Leeds. I know he has been back to Glasgow to get help with his injury, but unless he returns to Leeds, he has no club. I'm sure his loan contract with Leeds will include payments for the whole period of the loan, so he can get money and go to another club.
So he's available on a free transfer? Sounds like a potential Grayson signing...hope he isn't signed permanently.