Barlow was asked about rumours that Cowell is planning to return to the UK version of the show next series, having spent two years away launching the US version of the show on Fox.
"Could I judge alongside Simon Cowell if he came back? Mmm, I don't know," Barlow told The Mirror.
The Take That musician was also vague as to his possible future on the show, adding: "I have enjoyed this series more than last year, but the show feels like it has been going on for a year this time.
"If this is my last year, I've had a lot of fun and enjoyed every minute."
Barlow also confirmed reports that Take That plan to record another studio album, and will also join forces once again for another tour.
The X Factor semi-finals air this weekend (Saturday, December 1 and Sunday, December 2) on ITV1.
Watch Rylan Clark talking to Digital Spy about Gary Barlow and The X Factor below:
Photo gallery - 'The X Factor' quarter-final results show in pictures:
Copyright: Ken McKay/Thames/Rex Features