The couple have been dating for several months but Derulo told ET Online that they are divided on Idol finalists Jessica Sanchez and Phillip Phillips.
> American Idol poll: Do you want Jessica or Phillip to win?
"I'm Team Jessica and my girlfriend is Team Phillip," Derulo explained. "We have this little wager going on, so it's kind of cool.
"If I win, she has to massage my feet for ten minutes - and she hates feet - and if she wins, I have to cook her a meal, and I can't cook for anything. So I have to figure out what a recipe is!"
Phillips has admitted that he was "scared to death" before performing in the first part of the American Idol finale, while Sanchez has said that she considers both herself and Phillips winners.
The winner of American Idol will be crowned tonight when the show airs at 8/7c on Fox.