Craven fellow always has complaint (6,5)

'complaint' is the definition.
(yellow fever is a kind of disease)

'craven fellow always' is the wordplay.
I cannot really understand how this works, but
an anagram of 'fellow' is 'ellowf' which is within the answer.
'always' could be 'ever' (synonyms) and 'ever' is found in the answer.
A single letter 'y' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'has' is the link.

Can you help me to learn more?