My rabbit won't eat grass anymore

So as the title says, my rabbit has gone off eating fresh grass. He'll eat the dried grass that comes in his food though. It's been at least 2 months since he last ate fresh grass, however it hasn't been affecting him. He's still as energetic and playful as always, he eats all of his food and has no problems when it comes to doing his business.
My mother says I shouldn't be worried but I know how important grass is in their diet and I was wondering if this is a normal thing for them to go off it for a little while? It's not just the grass from my yard, I've picked grass from other places as well but he refuses to eat. I've also tried him with hay but he won't touch that either. If not, do you guys know any tips of getting him to eat fresh grass again?

PS: My rabbit is a very picky eater, so it could be that. But still, it makes me worried since he loved his grass.

If he still eats hay, he should be fine.

Hay is dried grass. What do you mean by "the dried grass that comes in his food?" Are you referring to pellet food? Is he only eating pellet food? Is he refusing to eat hay?

Rabbits don't suddenly stop eating something that they've always eaten unless something is going on. It would not be pickiness if it is something he used to eat. If he is refusing both hay and grass, then it is possible that he has a dental issue.

Yes, like Blue eyes said, it's likely to be dental problems. If he's not eating fresh grass or hay(dried grass), I would suspect possible molar spurs causing him pain when he eats those things(so he doesn't want to any more). It's common for dental problems to cause selective eating like that, where they will not want to eat one type of food because it hurts to eat it.
http://www.bio.miami.edu/hare/dental.html
http://www.medirabbit.com/EN/Dental_diseases/Differential/D_problems1.htm

I would suggest taking your bun to a rabbit savvy vet to have a dental exam done. If you don't already have a good vet for your bun, it's important that the vet you chose be a good rabbit vet so that the problem is diagnosed and treated correctly. Not many vets are very experienced with caring for rabbits properly.

If the vet finds spurs on the molars(which is likely), then your bun will need to have those sharp points filed/burred down so they no longer cut at the tongue or cheek. This usually will require a general anesthetic for the vet to be able to do this. You also want to make sure pain meds(usually meloxicam) are sent home with you afterwards, as a rabbit in pain is not likely to want to eat. And you may also need a syringe feeding mix to syringe feed to him for the first day or two if he won't start eating on his own after the procedure. If the vet is a good rabbit vet, they should go over all this with you.