NBA's Larry Johnson -- Alleged Deadbeat Dad ... To FOUR Baby Mamas!!

This might be a record ... but former NBA star Larry Johnson has been accused of being a deadbeat dad ... BY FOUR WOMEN AT THE SAME TIME ... TMZ Sports has learned.

Johnson wasn't just a stud on the court ... but the 46-year-old apparently lived up to his last name in the bedroom as well, siring 5 kids with 4 different women over the years.

It gets worse ... Johnson, the #1 overall pick in the 1991 NBA Draft, filed for bankruptcy in California earlier this month ... claiming he's racked up more than $300k in debts.

A chunk of those debts, according to the docs, are owed to the 4 baby mamas -- who claim LJ owes more than $120k in unpaid child support payments.

So, where'd all that Grandmama money go? We reached out to LJ for comment -- so far, no word back.