Mark Philippoussis's last coach (4)
I believe the answer is:
scar
'mark' is the definition.
(mark left by an injury)
'philippoussis's last coach' is the wordplay.
'last' indicates one should take the final letters.
'coach' becomes 'car' (as in a train coach or car).
The last letter of 'philippoussis' is 's'.
's'+'car'='SCAR'
(Other definitions for scar that I've seen before include "Mark left by healed wound" , "Steep rock - blemish" , "Limestone cliff or outcrop" , "Bare rocky cliff - injury" , "Evidence of an old wound" .)