Heartless manager replaced by a European (6)
I believe the answer is:
german
'a european' is the definition.
(I know that German is a type of european)
'heartless manager replaced' is the wordplay.
'heartless' says to hollow out the word (remove centre letters).
'replaced' indicates anagramming the letters.
'manager' with its middle removed is 'manger'.
'manger' anagrammed gives 'GERMAN'.
'by' acts as a link.
(Other definitions for german that I've seen before include "Alsatian" , "Proper name for 2" , "Middle European, for example" , "Composer, English? Yes" , "Helmut?" .)