Left English professor deceived (3,2)
I believe the answer is:
led on
'deceived' is the definition.
('lead on' can be a synonym of 'deceive')
'left english professor' is the wordplay.
'left' becomes 'l' (common abbreviation).
'english' becomes 'e' (abbreviation).
'professor' becomes 'don' (term for a university professor).
'l'+'e'+'don'='LED ON'
(Other definitions for led on that I've seen before include "persuaded to do something foolish" , "Took for a ride" , "deceived" , "Persuaded - tricked" , "Beguiled" .)