TMZ Sports talked to the 36-year-old MMA superstar days after the two towering men exchanged mostly pleasant, if not a bit tense, words at PFL 5 in Atlanta on Friday ... breathing new life into the fight fans want as much as any matchup in the sport.

"I think [it's possible]," Ngannou told us, adding a "cross-promotion" could be in store "in order to give the fans what they want."

"All the parties are down except for one," Francis said ... meaning the fighters and PFL are in, while the UFC is not (the promotion doesn't do cross-promotions with other companies).

Now that he's seen the bigger version of Bones Jones, we asked Francis about the heavyweight iteration of Jon.

"I will say I am more comfortable with a heavy Jon Jones than the Jon Jones of light heavyweight because of course, he gave an impressive performance against Ciryl Gane, but for the first minute, the first interaction and striking, he didn't look good."

Ngannou continued ... "He wasn't on point, as sharp as in light heavyweight, and for me that's the best -- I want Jon heavy! I want him heavier if he can put on more size."

Of course, Jones needed only half a round to beat Gane at UFC 285 in March, his first scrap at HW, but despite the win, Francis clearly wasn't impressed.

The Predator wholeheartedly believes Jon's in for a rude awakening if he thinks a fight with him would mimic the Gane bout.

"He never faced a guy like me, a real side heavyweight," Francis told us, explaining Gane was a perfect matchup stylistically for Jon.

"I think Ciryl was a perfect pro fighter to run into because there wasn't a threat. He's not a guy that's gonna knock you out with one shot."