Doctor captures headless French scientist (7)
I believe the answer is:
pasteur
'french scientist' is the definition.
(I've seen this before)
'doctor captures headless' is the wordplay.
'doctor' indicates an anagram.
'headless' means to remove the first letter.
'captures' with its first letter removed is 'aptures'.
'aptures' with letters rearranged gives 'PASTEUR'.
(Other definitions for pasteur that I've seen before include "Louis --, French bacteriologist" , "French chemist and biologist, d. 1895" , "French scientist" , "Louis ---, Fr. bacteriologist" , "He invented a method to stop milk causing disease" .)