Ex-UCLA Basketball Star Reeves Nelson -- Suing Sports Illustrated for Claiming He Pissed on Teammate's Bed

Former UCLA basketball stud Reeves Nelson says a Sports Illustrated writer slammed him with a defamatory article that claimed he ran amok on campus, and even peed on a player's bed ... and now TMZ has learned he's set to sue for $10 million.

If you don't remember ... Nelson was a 6'8'' stud at UCLA from 2009 - 2011, and by far the best player on the squad -- but was booted from the team in December 2011 after a second suspension for disciplinary issues ... including missing a team flight.

The March 5, 2012 issue of Sports Illustrated featured an article penned by George Dohrmann which claimed UCLA Coach Ben Howland let Nelson get away with everything but murder because he was "producing" on the court.

According to Nelson's lawsuit, the article claimed he was not punished after fighting with multiple teammates and intentionally injuring them during practice. The S.I. article also claims Nelson "urinated on [a teammate's] bed and clothes" -- purely as revenge for the player allegedly squealing about a New Year's Eve party.

But Nelson's high-powered entertainment lawyer Keith Fink says they can prove Dohrmann "recklessly and negligently failed to investigate the claims in the article." The lawsuit includes declarations from 18 UCLA players and ex-players who deny every allegation about Nelson.

In fact, former teammate Tyler Honeycutt says, "Nelson did not pile my clothes on my bed, and he certainly did not urinate on my clothes." According to the suit, most of the players say Dohrmann never contacted them -- and the 2 who were contacted denied the allegations.

The lawsuit further claims the S.I. writer has a longstanding beef with UCLA because he "publicly attacked UCLA's Baron Davis for driving a black 1991 Chevy Blazer, which Dohrmann publicly claimed had been purchased in violation of NCAA rules." NCAA investigators later shot down those allegations.