Dressage on Mr Big Leg

Today was typical spring weather, with sunshine, then a downpour. I didn't notice anything until I was grooming Duke at John's, but he nicked the inside of his right hind leg, so the outside of his hock was swollen and warm.
John watched us at first, and said Duke was bearing weight equally on all legs, so we had a flat lesson.
John had us work on bend, but not letting the circle collapse in; me sitting up and dropping my leg (something that was especially hard for me today), then we did some 10 meter circles, long side, lengthen, 10 meter circle, then a leg yield, turn into the line, and lengthen.
Duke was great, and was super sweet on the ground before we got going (while I was waiting for John to look at his leg).
John said bute tonight, watch for increased swelling, increased heat, or a temperature (then he needs antibiotics and it might turn into cellulitis) but let him walk around on it tomorrow because it will be good for the swelling to have the movement.