Machine Gun Kelly's fight with Gabriel "G-Rod" Rodriguez could spill from a hotel lobby and into a courtroom -- G-Rod's threatening to sue if MGK doesn't pony up for the beatdown.
G-Rod's attorney, Blake Dolman, tells TMZ ... the actor wants MGK to cut him a check or else he'll be gunning for millions in a lawsuit against the rapper to prove "the law does not allow him to hide behind others."
TMZ broke the story ... G-Rod got the crap beat outta him by MGK's crew in an Atlanta hotel lobby. The vicious attack stemmed from G-Rod calling Kelly a "p***y."
G-Rod's legal muscle believes Kelly's posse acted on behalf of the rapper and says "the intentional battery and assault caused serious and permanent injuries to G-Rod."
As we first reported ... Atlanta PD has ID'd at least 3 individuals involved in the attack and charged them with misdemeanor battery. Our law enforcement sources say MGK will NOT be charged with any crime because the investigation determined G-Rod triggered the fight.
Dolman calls the attack a calculated ambush when "all G-Rod wanted to do that night was return to his hotel room."