Martina may be an alien (7)
I believe the answer is:
martian
'an alien' is the definition.
(a lifeform from Mars)
'martina may be' is the wordplay.
'may be' is an anagram indicator.
'martina' anagrammed gives 'MARTIAN'.
(Other definitions for martian that I've seen before include "Sci-fi alien" , "One of H. G. Wells's invaders" , "Extraterrestrial" , "One living on red planet" , "Green man from the Red Planet" .)