Rookie footballer is an employee of course! (11)
I believe the answer is:
greenkeeper
'an employee of course' is the definition.
(someone employed by a golf course)
'rookie footballer' is the wordplay.
'rookie' becomes 'green' (green can mean inexperienced).
'footballer' becomes 'keeper' (goalkeeper).
'green'+'keeper'='GREENKEEPER'
'is' acts as a link.
(Other definitions for greenkeeper that I've seen before include "Person having care of golf course" , "Person caring for a golf course" , "Golf course maintainer" , "One maintaining a golf course" , "Golf course tender" .)