Hello, i have had chickens for about three years and sometimes the chicken will get hurt from random things roosters most of the time! If he is acting fine and not seeming to have any change I would not worry! If it seem's like its getting worse let me know, Though what you see seem's to not be a big deal at all and normal for roosters.Just in case I would also do reserch to make sure he is not showing any signs of fowl pox(which most of the time is yellow and crusty), also what is the tempture if it is pretty cold it could be frost bite so watch out for both of them.Good luck!