If due to illness one does not fast in the month of Ramadan, and after the month of Ramadan his illness is cured but another legitimate excuse arises such that he cannot make up the fasts until the following month of Ramadan, he must make up the fasts he did not keep; and based on obligatory precaution, he must also give one mudd of food to a poor person for every missed fast.
The same applies if in the month of Ramadan one has another legitimate excuse – other than illness – and after the month of Ramadan that excuse expires and until the month of Ramadan of the following year he cannot fast due to illness.