Retired San Antonio Spurs star Tim Duncan would be a "legit contender" if he chose to fight competitively in MMA, according to trainer Jason Echols.

Duncan – a five-time NBA champion, three-time Finals MVP, two-time NBA MVP and 15-time All-Star – has been training with Echols in the sport for nearly a decade.

And Echols praised the 41-year-old's ability away from the basketball court.

"He has a desire to learn and compete. He has the heart for it. He most definitely would be a competitor," Echols said in a Q&A with Bleacher Report.

"He's an animal. It's a different thing than what you see out on the court. The more intense the training gets, the more calm he becomes, which you've seen on the court. The way he executes the movements, he's a f****** monster."

The San Antonio-based trainer has been impressed by Duncan's power, athleticism, desire and ability to learn since the two started working out together.

"When he walked in the door, I could see that he was very hungry to learn martial arts, and his movement, his absorption of the martial arts was just phenomenal," Echols said. "You could really see the athleticism that existed in him already. It caught onto these movements, and he was able to absorb them better and pick it up better than the average person because of his athleticism. His size...it's incredible to watch him move. Now the world is seeing it."

Echols said that being only 5-foot-10 makes it difficult to handle Duncan in training.

"It's hard holding the mitts for him, hard getting hit by him," Echols said. "Even though he's lugging on me and not executing full power, just to take a wallop from his leg, it's quite an impact."

In fact, Echols once tore his bicep while working out with former NBA big man.

"He's so big and his elbows are like spears and his bones are really sharp," he said. "Just interacting and punching with him, I hit him with a right hook and his elbow caught the inside of my bicep and tore it right off, just from moving around. Whatever pace I'm at, he sets it."

Echols, though, is advising Duncan against fighting professionally.

"I wouldn't want him going out there and getting punched and kicked by some of those guys," he said. "But Tim would be a competitor."