He's already a lock to be considered one of the greatest of all time, one loss against another legend of the sport right at the end of his run isn't really gonna change that.
And let's be honest, his undefeated record is only really worth anything while he's still fighting - it's one of the selling points for his otherwise largely-dull matches. He's very close to retirement. What if Manny is the last guy he ever fights? Floyd-Manny 2 sells itself, no unbeaten record required.
I'm not saying this is how it's going to go down, I'm just wondering aloud if anyone is at least a little concerned that the outcome might not be on the level...