Competitor has viral problem (5)
I believe the answer is:
rival
'competitor' is the definition.
(I know that competitor can be written as rival)
'viral problem' is the wordplay.
'problem' indicates anagramming the letters.
'viral' anagrammed 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" .)