If it were me, I'd probably tell him, though I'd use a light touch. Rather than say I was pretty sure he'd got it, I'd say (something like) I sometimes wondered if he had it, and then sit back and wait to see his response. If he seems to recoil in horror, let it be, at least for the time being. If he seems receptive, offer to explain in more detail. It might be helpful to call it "high functioning autism," as that might come over as less of an attack on his pride than some of the other names. It shouldn't be too harmful to just raise the matter once in that way. I think it's a case of him either being interested or not, and if he's not, then all you can do is to back off and hope he'll be more interested at some later date.
I might be unusual. When it was first suggested to me that I may have Aspergers, I didn't feel offended or defensive. The person who told me taught autistic kids and had studied AS, and I suspected it may be just a case of her seeing autism everywhere because of her interest in the disorder, but I stayed objective and figured there could be no harm (and possibly a lot of good) in my taking a closer look. So I put in on my to-do list as a mildly important thing to look into, and a few days later I looked for an online test or two. I found the Aspie Quiz, answered the questions, and scored as "very likely an Aspie." I think it was easier to accept because I'd found out for myself rather than being spoon-fed the idea.
Ultimately, it might not be so awful if he rejects the idea. You'll still have your belief about what's causing his problem, and if you're correct, then you'll at least be able to understand his behaviour and deal with him more appropriately than anybody else. You'll be the one who doesn't expect thim to do things his brain wiring won't let him do, and the one who appreciates his autistic strengths and weaknesses, so you'll be in a position to do a lot of good even if he himself never knows why.