This is not a particularly helpful answer, but it depends on the variety, whether it is a dwarfed variety or not. My GC is full of the small sized rhohodendrons just now and those would be ok in a pot for a while.

That would be my answer too... depends on the variety and just how big your 'big' pot is. Remember it will need to be in ericaceous compost and semi-shade.

Thanks for that. It seems to be the common type of rhododendronso I guess I had better plant it I the garden, but I will have to dig in plenty of acid compost won't I as we have alkaline soil?

Yes Ericom you will need to create a very large planting hole and fill that with ericaceous compost. Don't plant the rhododendron any deeper than it was in the pot and remember they are a shallow rooted plant. Top dress each year with more ericaceous compost and feed with sequestered iron.