EXCLUSIVE

Former NBA star Mark Blount belongs behind bars ... for missing ONE measly child support payment -- this according to the guy's baby mama.

It's pretty strange ... considering most pro athlete child support actions are over tens of thousands of dollars in unpaid support -- Dennis Rodman, anyone? -- but Blount's ex says he merely owes $2,619.

The ex -- a woman named Sifika Mayfield -- filed a motion for contempt and enforcement, claiming Blount dropped the ball on a recent child support payment for their two sons, Mark and Mark (no joke).

According to Mayfield, Mark is supposed to pay $5,119 a month -- but in January, he only paid $2,500. Now, Mayfield wants a judge to throw Blount in jail and revoke his driver's license.

Mark filed his own docs soon after, claiming the reason he paid less is because one of his sons now lives with him ... and Blount personally pays for his schooling. Mark now wants the support order modified given the new living arrangements.