Conor McGregor actually had a shot against Floyd Mayweather ... but he would get straight-up SMASHED by Manny Pacquiao -- so says ex-UFC star Brendan Schaub.
We got Schaub -- an analyst on the MayMac media tour -- to weigh in on McGregor vs. Pacquiao with rumors of the super-fight swirling ... and he told TMZ Sports Conor doesn't have a chance in hell of upsetting Manny.
"I actually think it's a tougher fight for Conor," Brendan said. "Pacquiao's more of a pressure fighter, bigger puncher. Floyd Mayweather was the perfect matchup."
The big question -- will the fight actually get made?
Schaub gave us his 2 cents on that ... and what he'd do if he was in McGregor's shoes.