Dented muscle

My son was playing in a highschool football game about three weeks ago and got tackled.
His shoulder pad was shoved up under his armpit.
He had an indentation in the muscle (I guess the tri-cep)at the top underneath part of his arm closest to his armpit.
It hurt him at first and now he say it does not bother him.
My concern is, the indentation is worse now…. It is very noticeable.
Will this go away or should I take him to an orthopedic doctor? Thanks…..Liz