Stipe and the Pro Bowl defensive end focused on power work and and combinations in the cage earlier this week ... and Miocic says Garrett was loving every second of it -- and was crushing it!!
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"He's an absolute beast," Miocic tells TMZ Sports. "Whatever that dude does, he's good at."
We asked if Garrett would be able to hold his own in an MMA fight someday down the road ... and it's clear Stipe thinks he's got a legitimate shot.
"He's just gotta stand there and punch someone one time. That dude's got power. He's got a LOT of power."
Stipe has his own fight around the corner -- a rematch with Daniel Cormier at UFC 241 -- and he's got one message for DC.