After 40-year-old Manny put a hurtin' on Keith Thurman this weekend, there's a huge buzz about a MayPac II rematch ... following the first superfight back in 2015.

Roach, who's been training Pacquiao for years, says Manny and the entire team is down ... if Floyd is man enough to get back in the ring.

"[Floyd] would be a fight we'd want. I'd like to get that one back one more time. I know we can do much better. We had an injury in that fight, but regardless, we lost a close decision. I know Manny can do much better than that."

Remember, after their May 2015 fight, Manny revealed he suffered a shoulder injury in training camp which he says held him back in the main event.

But now, Manny's healthy -- and looked awesome in the Thurman fight -- and Roach ain't all that impressed with the work Mayweather's done inside the ring over the past few years.

"Floyd's last couple of fights against a kickboxer and whatever the other guy was [Conor McGregor] he wasn't too impressive," Roach tells us ... "I think it's a good time to catch him right now."

Freddie says Manny was planning to call out Floyd in the ring after he defeated Keith Thurman ... but Floyd bolted out of the arena.

Of course, 42-year-old Floyd keeps insisting he's retired ... but c'mon, you really think he'll turn down another $300 million payday?!?

"I do think it could happen, yes. Probably not 'til next year. But, the thing is, it is a big fight out there. And, again a fresh Manny with no injuries, I love that fight."