Competitor has viral problem (5)
I believe the answer is:
rival
'competitor' is the definition.
(I know that contestant is a type of competitor)
'viral problem' is the wordplay.
'problem' indicates an anagram.
'viral' with letters rearranged gives 'RIVAL'.
'has' acts as a link.
(Other definitions for rival that I've seen before include "Person in direct competition" , "Close competitor" , "Adversary or foe" , "Contestant you hope to defeat" , "Challenger, competitor" .)