Dancer's career regressed before scan number five (7)
I believe the answer is:
nureyev
'dancer's' is the definition.
(Rudolf Nureyev)
'career regressed before scan number five' is the wordplay.
'career' becomes 'run' (career can mean to run or move out of control).
'regressed' is a reversal indicator (to regress is to go back).
'before' means one lot of letters go next to another.
'scan' becomes 'eye' (I've seen this in another clue).
'number five' becomes 'V' (Roman numeral).
'run' backwards is 'nur'.
'nur'+'eye'+'v'='NUREYEV'
(Other definitions for nureyev that I've seen before include "Rudolf -, Russian ballet dancer" , "Rudolf -, Russ. dancer" , "Fonteyn's dancing partner Rudolf" , "Austrian ballet dancer, 1938-93" , "Acclaimed Russian ballet dancer" .)