Actually Natukiro, your hammy looks like a nice size in your avatar. He is the same hammy, right? Not every hammy likes a wheel. I think you just have a contented hammy who just likes to be a couch potato. I'd really not worry as long as he is eating and drinking and pooing okay. You could try letting him wander in a play pen and see if this encourages him to be more active. Also, Cupcakes idea of trying a flying saucer is a good idea. Even if these ideas don't work, I still wouldn't worry. Hammies are individuals, just like people. He may be marching to a different drummer.
Or sleeping to one, at any rate.