Pac has only ever been KO'd by body punches. He got a body made of khanium. But since everyone else except bantam Thai midget are too big to hit his body he is 100% safe.
Margarito stepped in the ring against him as a middleweight, and he couldn't get the job done. Of course it's possible for anybody to get knocked out. This same thing was being discussed before Oscar, Hatton, Cotto, etc. It was constantly "Pac is fighting somebody way to big, and gonna get knocked out". I wouldn't bet on him getting KOd anytime soon that's for sure. Marquez puts on a few pounds of muscle, and suddenly he's going to knock the world out. Bradley has lots of muscle and it didn't mean much.. Guy hits like he got pillows in his gloves. Granted, maybe it'll be more functional on Marquez.
Manny's chin and body hasn't been tested in the last couple of years only by a lone bodyshot by Margarito that hurt him and the other times is when he's fought Marquez. It doesnt matter if its even a heavyweight it matters who's he sparring/fighting with. I'd take my chances with a featherfisted HW than a heavy fisted featherweight!
This is how Mayweather vs Manny would look like. [url]https://www.youtube.com/watch?v=Hvv3yD-o3p8[/url] the midget being Manny.
It will be very difficult for either to get a stoppage win, but it isn't impossible. Now mentioning that Martinez can't knock out Pac, is ****ing ******ed. Sergio would brutally KO Pac.