Doubt Mike is generous (9)
I believe the answer is:
misgiving
'doubt' is the definition.
(I know that misgiving is a type of doubt)
'mike is generous' is the wordplay.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'generous' becomes 'giving' (similar in meaning).
'm'+'is'+'giving'='MISGIVING'
(Other definitions for misgiving that I've seen before include "Qualm, scruple" , "Feeling of doubt" .)