Contestant has viral problem (5)
I believe the answer is:
rival
'contestant' is the definition.
(I know that rival is a type of contestant)
'viral problem' is the wordplay.
'problem' indicates an anagram.
'viral' is an anagram of 'RIVAL'.
'has' acts as a link.
(Other definitions for rival that I've seen before include "Competitor; be as good as" , "Close competitor" , "Be equal to in quality" , "Compete with" , "Emulate" .)