Workmate plays cello and gets a fever (9)
I believe the answer is:
colleague
'workmate' is the definition.
(I've seen this before)
'plays cello and gets a fever' is the wordplay.
'plays' indicates an anagram.
'and gets' means one lot of letters go next to another.
'a fever' becomes 'ague' (I've seen this before).
'cello' with letters rearranged gives 'colle'.
'colle'+'ague'='COLLEAGUE'
(Other definitions for colleague that I've seen before include "Fellow worker" , "Business co-worker" , "Fellow-worker" , "China, perhaps" , "Workmate" .)