Don't call it a comeback -- cause it's a looongshot -- but Stephon Marbury says he's gunnin' for an NBA return!

The 40-year-old announced the news on social media, adding that -- "I still have a lot of go in me as a player and at 40 being able to play at a high level is a gift."

Remember ... Starbury left the league 8 YEARS ago after a string of sketchy off-court incidents -- highlighted by him eating Vaseline straight out of a jar.

He famously packed his bags for China ... and became the most legendary player in Chinese Basketball Association history (for real, dude's already got his own statue).

Now, Marbury says he's ready to "turn towards the last page of my basketball diary that I've been writing since 95 when I left Lincoln High."

Will a team take a chance on him? We'll see ...