You bet! You may, and it's strongly recommended unless you are comfortable with the opinion of the employee's doctor.
First, by sending the employee to the doctor, you can verify the need for the reasonable accommodation. (Honestly, this is not a big deal because challenging the existence of an employee's medical condition is a losing battle most of the time.)
Second, you can determine which types of reasonable accommodation are appropriate and have the best chance of working. This is a huge deal. Here are a few ways to make sure it works:
Please see full publication below for more information.