A man named Matthew Graham has filed a lawsuit against the singer, claiming he was working Akon's show at BayFest music festival in Alabama back in 2009 -- when Akon "negligently or wantonly leapt into the overcrowded mass of concertgoers" and struck him. See video below (scroll to 00:50).
Graham says he sustained severe and permanent injury to his knee, back, head, and body during the incident -- and is now physically disabled. He doesn't specify the extent of his disability.
Graham is suing for medical expenses, lost wages, physical pain and mental anguish -- demanding unspecified damages. He is also suing BayFest, Inc.
Graham's lawyer Tyler Mann tells TMZ ... "We hope to achieve fair and adequate compensation for what occurred to him."
Calls to Akon's camp weren't returned.