Genuinely concerned with friend (6)
I believe the answer is:
really
'genuinely' is the definition.
(I've seen this before)
'concerned with friend' is the wordplay.
'concerned with' becomes 're' (re can mean regarding, concerning).
'friend' becomes 'ally' (synonyms).
're'+'ally'='REALLY'
(Other definitions for really that I've seen before include "Actually, no kidding" , "are you sure?" , "surprised expression" , "In truth - join forces again" , "Genuinely" .)