NBA's Damian Lillard -- I'm Dropping A Rap Album!!

He just dropped a new song, but NBA superstar Damian Lillard says there's a lot more to come -- 'cause he's planning on dropping his very own ALBUM in the very near future ... TMZ Sports has learned.

The Portland Trailblazers guard is widely considered the best rapper in the league -- and famously created "#4BarFriday" -- which became a freestyle hip-hop phenomenon on social media.

In fact, he put out a song called "Soldier in the Game" on Monday -- and we're told it's just a taste of what he's got cooking in the studio.

Dame tells us he's been working on a solo project -- and is hoping to release it very soon.

"It's definitely in the works. Rap is another passion of mine."

Don't worry Portland -- Dame says his primary focus is still BASKETBALL ... and his rap career doesn't get in the way of his training.

"I spend 80% of time thinking about and working on basketball things. A percentage of what’s left goes into me expressing my story through music."