You never know, they may win the premiership and champions league this year, then the domain will be worth quite a bit! But I don't actually think that will happen!
I personally would keep the .com for a while and sell the .co.uk. You should be able to get quite a bit more than the reg fee from a chelsea fan/site owner.
Then if/when he moves to another club you could still sell the .com no matter what country his new club is in.