He may just be a very lazy lazy boy Neomy, I certainly have had hamsters like this. If you are unsure of course I would suggest that you take him to the vet to check his health to make sure he is fine.
Of course you could try giving him some different playthings, changing his cage around, to see if that gives him a bit of interest.
I also tend to make my hams work a bit, such as putting their bedding in the middle of the cage so they have to move it to where they want it, and rather than putting all the food in the bowl, scattering and hiding it may make him spend time finding it and putting it exactly where he wants it