An employee is entitled to FMLA leave if he has “a serious health condition that makes the employee unable to perform the functions of the position.” 29 U.S.C. § 2612(a)(1)(D). This decision holds that an employer may defend a claim by the employee by introducing evidence–other than a medical expert’s opinion–to show that despite the employee’s medical expert’s contrary opinion, the employee is still able to perform the functions of his position.