Worried it may be imperfect (5)
I believe the answer is:
tense
I believe this clue is a double definition.
'worried' is the first definition.
(I've seen this before)
'it may be imperfect' is the second definition.
(I've seen this in another clue)
(Other definitions for tense that I've seen before include "Nerve-racking" , "In a nervous state" , "Could be present" , "Rigid, or grammatical time" , "Maybe future" .)