I think you should make the call! Also, you might try some hydro-therapy on it. Just let the hose run on it for 10-15 min and it might calm down the swelling. If it started w/a cut and the swelling is caused by infection you want it to be seen asap, don't want an infection in the knee joint! I am not sure DMSO is the greatest thing to be putting on it, but I don't know the whole situation. Is he limping at all? Is it warmer than normal? Is he eating and drinking ok?