Evander Holyfield actually traded punches with a young Andy Ruiz back in 2011 ... when Andy was only 19 ... and the "Real Deal" tells TMZ Sports he knew back then the guy was a stud.
"He's good, we sparred when I was 46 and he was 19," Holyfield said (Ruiz was actually 21 at the time).
"He showed that he was good then. I'm sure when people continue to practice, they work, they continue to get better."
The footage of the 2011 sparring session is pretty great -- the two are both in headgear, but they trade some pretty solid shots ... you can see the potential in Ruiz.
At the time, Holyfield was still an active fighter -- he beat Brian Nielsen by way of TKO in the 10th round during their May 2011 heavyweight bout. It was Evander's final pro fight.
On the other hand, Andy's pro career was just getting started at the time ... by the end of 2011, he was 13-0 and was getting a reputation as a legit threat in the boxing world.
Of course, Andy went on to upset Anthony Joshua in June 2019 to win 4 heavyweight titles ... and Holyfield says he's excited for the rematch.
So, who would win a Holyfield vs. Ruiz heavyweight fight???
We asked Evander ... and even though there's no way to find out, the 2011 sparring video makes us think it would've been a GREAT fight!!!