Believe in cure ultimately following surgery (5)
I believe the answer is:
opine
'believe' is the definition.
(thesaurus)
'in cure ultimately following surgery' is the wordplay.
'ultimately' indicates one should take the final letters.
'following' means one lot of letters go next to another.
'surgery' becomes 'op' (short for operation).
The last letter of 'cure' is 'e'.
'in'+'e'='ine'
'ine' after 'op' is 'OPINE'.
(Other definitions for opine that I've seen before include "Express one's view" , "Think - express a view" , "Express one's opinion openly" , "Express a point of view" , "Conjecture" .)