Remiss in supporting worker (10)
I believe the answer is:
behindhand
'remiss' is the definition.
(thesaurus)
'supporting worker' is the wordplay.
'supporting' becomes 'behind' (I've seen this before).
'worker' becomes 'hand' (hand is a kind of worker).
'behind'+'hand'='BEHINDHAND'
'in' acts as a link.
(Other definitions for behindhand that I've seen before include "From which one might snigger" , "Late or slow in doing something" , "in debt" , "not keeping up with schedule" , "Late - in arrears" .)