"American Idol" alum Haley Reinhart's pal -- who was choked out by bouncers at a bar in Illinois -- is now putting the squeeze on them ... legally speaking.

Alan Chislof just filed a lawsuit against the Lamplighter Inn Tavern & Grille and one of its bouncers, Adam Sobanski, for the July beatdown that left him with what he says are permanent injuries. 

We broke the story ... Alan claims he was choked so badly by Adam and other security that night, he suffered a concussion, a facial laceration near his right temple, a bad cut above his left eye, facial bruising and hematoma. Haley was arrested soon after when she allegedly punched one of the bouncers in the scuffle.

THE TAKEDOWN
TMZ.com

In the docs, obtained by TMZ, Alan's lawyer, Mark A. Brown, says Adam's responsible for his injuries and Lamplighter is responsible for negligently hiring and not properly training him to be a good security guard (i.e. not beating the crap out of its customers). The dude's already facing 2 felony counts for the altercation.

Still, Alan's asking for an unspecified amount in damages.