Pity flu turned out to be embarrassing (8)
I believe the answer is:
shameful
'be embarrassing' is the definition.
(I've seen this in another clue)
'pity flu turned out' is the wordplay.
'pity' becomes 'shame' (synonyms).
'turned out' is an anagram indicator (turn out can mean to organise).
'flu' is an anagram of 'ful'.
'shame'+'ful'='SHAMEFUL'
'to' is the link.
(Other definitions for shameful that I've seen before include "Reprehensible" , "Embarrassing" , "Humiliating" , "Disgraceful" , "Dishonourable" .)