We spoke to the heavyweight champ on the heels of Jon's failed steroids test ... and Stipe says he hadn't heard of a potential matchup with Jones till Dana White mentioned it to reporters.

"I had no idea. I was like, 'That's news to me,'" Miocic told TMZ Sports.

Stipe's not ruling out a fight with Jones down the road -- but with JJ sidelined for who knows how long, he says he's looking to pull a Conor McGregor ... and fight heavyweight boxing champ Anthony Joshua!

Stipe would be a BIG underdog, just like Conor was against Floyd Mayweather ... but tells us he can hang with Joshua, no problem.

Dude was a Golden Gloves champ ... so never say never.