 [ Symptoms ] how does exercise affect my bones [ Disease ] mono can cause the liver andor spleen to enlarge to the point that it is vulnerable to a blunt injury not uncommon in soccer assuming that she does not have liver or spleen enlargement and her liver enzymes a blood test are normal she may be able to play the doctor really should not have left it up to you i agree this is really a medical decision based on physical exam findings mono can be mild and mono can be very problematic so unfortunately without knowing the details of her particular case and of course those critical physical examination and lab findings you will need to put the ball back in the doctor is court to make this decision