Lethal -- real name Chris Matthews -- came to the conclusion after working with the "Hustlin'" artist earlier this month before he had to take a private jet to Las Vegas.

Matthews spent about an hour with the celeb ... and he was so impressed with Ross' work ethic, he said the dude could've been "elite" on the hardwood if he had chosen ball over hip hop.

"As soon he got out of the car, he didn't waste any time," Matthews said of Ross. "He was looking to train. He only took two breaks. He wanted to learn."

Matthews, of course, didn't say an NBA career would've been in Ross' future if he had picked basketball at a young age ... but he explained to us the 47-year-old could've potentially made it as a college hooper if he wanted.

"I feel like people don't realize Rick Ross is pretty tall and anything that somebody put their mind to, they're capable of," Matthews said.

"What I saw from somebody, the age that he's at, that he was learning so fast I think he could've been capable at a young age to play at an elite level as far as high school and college."

Matthews knows a thing or two about A-listers with hoops skills ... he's trained a bunch of celebs over the years -- and told us guys like Future and Mark Cuban have some underrated games.

"When I was training Mark Cuban a few months back," Matthews said, "I felt like you can tell at a young age he was one of those guys that was always gonna bring it on defense, always gonna bring the intensity."

When the 38-year-old is not helping celebrities with their jump shots ... he's going nonstop at giving back to his hometown Washington D.C. -- telling us he recently donated $18K to three different schools in the DMV area.