My Son Was Playing Soccer And Bumped Knees With Other

my son was playing soccer and bumped knees with other player. He said it hurt at first but hasn't hurt since initiation and he has been running and kicking.. It shows a quarter sized bruise no swelling. I can have him sit out for a while or should I let him loose. HE IS 11 years old and great soccer player and has good knees.. Looks like impact injury to inside of knee right at joint.