Cops are now investigating Ja Morant after the NBA superstar was seen on video over the weekend brandishing a firearm ... TMZ Sports has learned.
A spokesperson for the Glendale Police Department in Colorado tells us they launched the probe into the matter shortly after Morant went on Instagram Live from what appeared to be a strip club with a gun in his hand.
According to the spokesperson, cops "have confirmed the incident took place at a bar in Glendale" -- adding, "We are investigating the matter."
No further details surrounding the probe were given.