Ryan Leaf's domestic battery arrest was NOT substance abuse-related ... so says the ex-NFL QB's attorney, who tells TMZ Sports the former San Diego Charger is still "100% sober."
There had been some concern after 44-year-old Leaf -- who has battled drug and alcohol problems in the past -- had suffered a relapse that led to his arrest on May 22.
But, when we spoke to David Greenberg of the Law Offices of Soda & Greenberg ... he told us that just wasn't the case at all.