Hi,
Firstly, I'd check the paw pad for a thorn or splinter that would hurt if he were weight bearing on it. The only time I've seen Reggie limp was when I pushed him off from jumping up on me sitting in a chair and he landed on his foreleg awkward, limped for just enough seconds for me to get worried then went back to normal again! I've had him from 7 weeks old and haven't experienced your situation so assuming the paw pad check is clear I would go to the vet to rule out anything more serious who may prescribe some anti-inflammatories or painkillers. I tend to avoid vets so wouldn't suggest it unnecessarily. Best wishes x