Unenthusiastic
It’s an adjective and it means not having or lacking enthusiasm. If someone is unenthusiastic about something it means they are feeling indifferent, apathetic, passive, phlegmatic, lukewarm, listless, languid, lethargic, emotionless, perfunctory about it.
I’m unenthusiastic about having Malcolm on the team.
unenthusiastic
It is an opposite meaning of enthusiastic. A type of scepticism. If someone doesn't believe in success.
John was unenthusiastic but gave it a chance for win
Unenthusiast
(n.) a person who is unenthusiastic about everything and defines their personal by such an intense lack of enthusiasm
Person 1: “Why are you being so mopey?”
Person 2: “I dunno, I’m just an unenthusiast”
Person 2: “I dunno, I’m just an unenthusiast”