If my employer came to me and said "sign with us now or we'll turf you out to out rivals" having already known that I didn't want to discuss contract details until a certain period (which is well within my rights), it'd give me a great deal of incentive to leave.
That. Ultimate. Achieves. Nothing! (Nothing good anyway)
If he stays he will stay. If he wishes to leave at season's end he may very well do so. If he is given an ultimatum having not made up his mind it will only push him one way, IMO.
And I'm sorry, but your post before was pure rubbish. "Be strong on this" - it doesn't apply in this context at all.