Close to losing knight's attention (3)
I believe the answer is:
ear
'attention' is the definition.
(having someone's ear is having their attention)
'close to losing knight's' is the wordplay.
'close to' becomes 'near' (close to means nearby).
'losing' indicates named letters should be taken away.
'knight' becomes 'N' (chess abbreviation).
'near' with 'n' taken out is 'EAR'.
(Other definitions for ear that I've seen before include "Head of, eg, corn" , "Seed-bearing part of wheat" , "Organ involved with balance" , "'Give every man thine ..., but few thy voice'/Hamlet" , "Organ inside heart" .)