Can we fire? Doctor added 3 months to injured worker’s restrictions

Q. One of our employees broke his ankle while on vacation last summer and he has still not fully recovered. He has been on work restrictions from his physician since the accident, and those restrictions limit his ability to perform job duties that involve walking, standing or lifting. We have accommodated the restrictions, but we recently received a note from his doctor asking us to extend the restrictions for another three months. Do we have to do that or can we simply terminate the employee?