The all-star edition of the reality show features stars from the past six seasons competing for a $100,000 prize.
A source said Knight began to "lose it" while locked in the "Surreal Life" house and had his brother, Jonathon, come and get him, the New York Daily News reported Tuesday. Knight reportedly did not give his housemates any reason for his exit.
VH1 said the singer left because his grandmother died, while Knight's representative told the Daily News a family illness required his presence in Boston.
Exploding whale video goes viral on Internet
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'