My 12 Year Old Son Just Informed Me That His

my 12 year old son just informed me that his left testicle hurts. mild pain all the time and then more severe as he does activities. it also hurts he says when he touches the left testicle. When he touches his left testicle he says he gets a pain in his lower left side just below the waist line. a week ago a soccer ball was kicked in to this area very hard and at a short distance during a game. The pain caused him to come off the pitch but, it only started hurting today - 7 days after the event. Thank you, Robert