AFC North quarterbacks better watch out ... 'cause Cleveland Browns star Myles Garrett has been training with Stipe Miocic ... and the UFC heavyweight says he was blown away by his power!!!
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!!
"He's an absolute beast," Miocic tells TMZ Sports. "Whatever that dude does, he's good at.