Hell, my ankle has been bothering me for the past 7 years. Can't rotate it around without sounding like a cement mixer. After falling down a set of stairs and twisting my ankle twice (first one the 1st step and second on about the 5th - now that was painful), it's never been the same.
Better a light sprain in training (obviously showing that his ankle isn't ready) than having another 300 lb lineman fall onto it causing serious structural damage to the ligaments and bone connectivity. Keep him out if he's still limping.