If it's just the sneezing and no other symptoms,he should be fine. My girls only really sneeze when their pellets aredusty or if they put their noses in their water.
Are his pellets dusty? You could try sifting out his pellets and maybe shaking out his hay to minimize the dust.
If there is not-clear nasal discharge, that is asign of a respritory infection. Now, the problem is thatbunnies groom themselves seemingly nonstop, wiping away thedischarge. I've been advised to also check the insides ofwhat are basically bunny wrists, the parts of their arms they use towipe their noses.