The music mogul is currently judging the upcoming season of The X Factor USA alongside Spears and fellow judges Simon Cowell and Demi Lovato.
When asked if he thought the 'Hold It Against Me' singer could have won the competition had she ever competed, Reid told TMZ that it would "depend on who the judges were".
He added: "If I was a judge, she would have won."
Reid also revealed that he enjoys working with Spears, who signed on with Lovato to replace former judges Paula Abdul and Nicole Scherzinger.
"Britney is doing amazing," he said. "She's a lot of fun."
The producer had no comment on recent reports that he, Spears, Lovato, and guest judge Louis Walsh walked out on an audition in Kansas City, teasing: "You'll have to watch the show."
The X Factor USA returns to Fox this fall.
Photo gallery - 'The X Factor' USA judges arrive in Kansas: