Termination Due to Medical Leave

I am writing to ask for your kind advise on how to let go an employee who is constantly sick? We hired an employee who has used up all his sick leaves during the probationary period. Is it legal to fire someone over this issue? What should I pay attention to?

Please note that the entitlement of medical leave is not based on the probation period but is based on the length of service.

The company cannot fire some one who is sick :)
Few advices for you to handle such cases:
1) You may want to work with your line manager to constantly talk to employee and set the target for him, so the company can measure his/her performance. Proper disciplinary procedure such as verbal warning, warning letter, final warning and termination can be carried our based on poor performance..... but not based on his/her illness

2) Take a look of the Medical Leave, whether clinic hopper? talk to the employees, talk to the company doctor (if any). Talk to employee and limit him to the clinic he/she can visit, which he/she deem acceptable.... try to manage from there, if you know what I mean :)