Is s/he limping? If it would be footrot - they would be limping, and there would be a characteristic smell (once smelt never forgotten!), but also footrot occurs in-between the toes (it starts usually as scald), and then starts to rot their sole, sometimes their heels.
If there is no limping, no visible abscess(
spelling), I would wait a couple of days and see if anything develops, also - just on one leg or all four?