Left a learner at the doorway (6)
I believe the answer is:
portal
'the doorway' is the definition.
('portal' can be a synonym of 'doorway')
'left a learner' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'port'+'a'+'l'='PORTAL'
'at' acts as a link.
(Other definitions for portal that I've seen before include "'Doorway, entrance (6)'" , "An imposing door or gate" , "An imposing gate or doorway" , "Grand and imposing entrance" , "Gate, entrance" .)