O'Dea signed a new deal with Celtic before going on loan.
There may be many different reasons for that
Possibly there was no other club willing to give him a 3 year contract at this stage but quite a few clubs were willing to take him on loan, hopefully he went for a club that he has the best chance to start.
He is still a young lad. 3 years contract security with Celtic and out on loan, is good going.