What Causes An Indentation In The Outer Thigh Muscle?

About a month ago I noticed a small indentation running laterally in my right thigh muscle. Since then it have gotten dramatically larger and deeper. There is no bruising and it doesn't hurt. I have never injured my leg. I am 24 years old am not over weight, I'm in good shape with muscular legs. It literally looks and feels like part of my thigh muscle has been scooped out. Any ideas what could have happen?