Mavis sadly concealing love for sci-fi writer (6)
I believe the answer is:
asimov
'sci-fi writer' is the definition.
(I've seen this before)
'mavis sadly concealing love' is the wordplay.
'sadly' indicates anagramming the letters.
'concealing' indicates putting letters inside.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'mavis' anagrammed gives 'asimv'.
'asimv' enclosing 'o' is 'ASIMOV'.
'for' is the link.
(Other definitions for asimov that I've seen before include "Author of "Three Laws of Robotics"" , "Isaac --, sci-fi author" , "Isaac -, US sci-fi writer" , "He wrote about robots" , "Isaac ---, SF author" .)