My Gerbil has a cut around his eye, what do I do?

He's in the cage with two others. They came from the same litter. They tussle around every day, but I don't know if it's play fighting or real fighting. It only lasts for a few seconds then they go back to doing whatever, but I just noticed that one of them has a little red cut going around half of the outside of his eye. What do I do? Should I worry?