Hard to say not knowing what else he's got (diabetes? fat? heart? etc).
All I'd say is this. Get to the GP fast, and don't be fobbed off without an x-ray.
I had a painful swollen ankle 18 years ago, wouldn't get better, tight-fisted GP wouldn't send me for an x-ray (fund-holding practice, so it would cost him money).
Ended up losing the leg!
My fault initially, as at the time I was an alcoholic, but make sure you get proper treatment!
Good luck, hannah40.
A