He has tuberculosis and is unable to fast
Question

A person has been affected with tuberculosis since three years. Two Muslim doctors have decided that he should not fast due to this disease. Is he allowed not to fast then?.
Praise be to Allah.As Muslim doctors have determined that he will be harmed by fasting, then it is permissible for him not to fast, but he should make up the missed fasts after he recovers, in sha Allaah. 
End quote. 
Fataawa al-Shaykh Muhammad ibn Ibraaheem (may Allaah have mercy on him) (4/181, 182). 
But if he cannot fast after that, then he must feed one poor person for each day.