Under a strain at present (5)
I believe the answer is:
This clue is a double definition.
'under a strain' is the first definition.
'present?' is the second definition.
'at' is the link.
(Other definitions for tense that I've seen before include "imperfect, perhaps?" , "Anxious, high-strung" , "Nervous or tight" , "Taut - timely verbal indication" , "In a nervous state" .)