EXCLUSIVE
Walter Lee claims in the lawsuit -- obtained by TMZ -- he was walking on the Sunset Strip a year ago just before midnight when Justin was cruising down the street and struck him.
As we previously reported ... Bieber was leaving the Laugh Factory with Lil Twist in the passenger seat.
Lee claims his injuries are severe -- lacerations, hematomas, deep abrasions on his left knee and leg and deep venous thrombosis.
He says he's been saddled with hospital and other medical bills.
Justin was actually investigated for hit-and-run but cleared.
