Wishes Future Zahir Happy Bday

Baby Future is not a baby anymore -- and Russell Wilson just sent his stepson a heartfelt message on his 8th birthday ... calling him the "greatest blessing in the world."

Russ was spreading love to the lil man bright and early on Thursday -- posting a side-by-side pic of the two on social media ... expressing what Ciaras child with rapper Future means to him.

"Happy Bday Future!" Russ said on Twitter. "8yrs old! You are the greatest blessing in the world to me!"

"So full of the fruit of the Spirit of Jesus! Love, Joy, Peace, Forbearance, Kindness, Goodness, & Faithfulness! Galatians 5:22."

He added ... "Mommy, Daddy, Sienna, & Win love you to Heaven & back!"

Of course, Russ relationship with the rappers son has sparked drama in the past -- Future previously called the Super Bowl champ out for being seen out in public with his son ... saying, "At the end of the day, Im not for the publicity stunts. Leave my son out of the publicity stunts. Just leave him out of your relationship."

No word on Russ and Futures status now ... but as we previously reported, the Wilsons booked it after the "I Never Liked You" spitter popped up at a Super Bowl party earlier this year.

Russ also shared a pic of Future Zahir rocking a baseball jersey and holding a trophy ... so the kid is definitely following in his stepdads footsteps.

While Wilson was a two-sport athlete -- he was drafted by the Rockies in 2010 -- he seems fully supportive of Futures future on the diamond, once calling him "The next Griffey Jr."

Happy birthday, kiddo!!