Taking ill again with flu, sent off (9)
I believe the answer is:
resentful
'taking ill' is the definition.
(I've seen this before)
'again with flu sent off' is the wordplay.
'again' becomes 're'.
'with' says to put letters next to each other.
'off' indicates anagramming the letters.
'flu'+'sent'='flusent'
'flusent' with letters rearranged gives 'sentful'.
're'+'sentful'='RESENTFUL'
(Other definitions for resentful that I've seen before include "Embittered - nurse left (anag)" , "Feeling bitterness" , "Bitter" , "Disgruntled" , "Bearing a grudge" .)