A photo of the Quebec native decked out in a VGK uniform popped up on the T-Mobile Arena jumbotron ahead of Game 5 of the Conference Finals on Tuesday ... with many wondering if Dion had actually ditched her roots for Sin City.

Of course, home teams love to do this in games -- showing fake pics of their opponents' most famous supporters rocking their threads really gets the fans riled up.

While the image clearly appears to be altered, Dion felt the need to set the record straight on Thursday ... saying, "By the way, I have nothing to do with this photo ... And you know what photo I'm talking about!"

It wouldn't be that farfetched to think Dion is a Golden Knights fan -- after all, her massively successful residency is in Vegas ... and she HAS been spotted wearing their jersey in the past.

But, as the Habs and Knights are set to face off in a heated Game 6, Dion had to make sure her team knew who she'd be rooting for.

Silly?? Yes. But, did you REALLY think we were gonna pass up on getting a Celine Dion sports crossover?!

The Habs are one win from making the Stanley Cup Final for the first time since 1993 ... so you could say it's all coming back to (them) now.