He will be just several weeks shy of his 35th birthday when he steps into the ring with Rios on November 24, and Roach insists that when it is time to stop, he will know.
"It's over, 100% [if Rios knocks Pacquiao out]," Roach told Yahoo. "We have a deal, when I tell him it's over, he'll say it's over and that's that.
"The thing is, people look at the losses and think the reason is that he's getting old. That's not the case. Look, we all thought he beat Bradley, so throw that out. In the Marquez fight, I thought he was doing well and was looking like he was going to win when he made a mistake and ran into a shot.
"That happens, that's boxing. It didn't happen because his skills aren't the same as they used to be. It happened because he made a mistake."
The two men who beat Pacquiao in his last two outings will face each other on October 12.