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Terrell Davis tells TMZ Sports if CBD was around when he was playing for the Denver Broncos ... his Hall of Fame career would have lasted a lot longer than it did.

TD famously broke into the league as an immediate superstar in 1995 ... rushing for more than 6,000 yards in his first 4 seasons.

But, a knee injury ultimately sapped him of his prime years ... forcing him to play in just 17 games in his final three seasons and retire at just 29 years old.

Now ... Davis tells us if CBD was around back then -- he's confident his career would have been saved.

"I believe so, because any time you can help your body heal -- you can take out the swelling, the inflammation and you can do it in a way that's natural -- I feel like absolutely it would have assisted in that."

Davis says he knows this because he's a regular user of the drug ... and, in fact, he is coming out with his own CBD product called Defy that is set to launch this spring.