Jamal Anderson -- Locked Up In Georgia After Gas Station Penis Debacle (MUG SHOT)

Ex-NFL star Jamal Anderson is back behind bars ... stemming from a bizarre incident at a Georgia gas station when the former Falcons star allegedly whipped out his penis in front of the clerk.

TMZ Sports broke the story ... Anderson was issued a criminal trespassing ticket for the incident -- and now we've learned a warrant was issued for his arrest because officials believe he violated his probation.

Turns out, Anderson was on probation from a 2014 DUI conviction -- and part of the probation required him to stay out of trouble with the law.

Anderson was taken into custody on December 19th and is being held at the Gwinnett County Detention Center until his hearing in January ... when a judge will decide his fate.

We spoke with Assistant Solicitor General Jennifer Scacco who told us Anderson's arrest is directly related to the gas station incident.

It's just the latest legal issue for Anderson who's been arrested multiple times since he wrapped up his NFL career in 2001.