Shaquille O'Neal REJECTED from Nightclub -- You're Dressed Like a Schlub!!!

Shaquille O'Neal couldn't power his way through the lane at a New York nightclub this weekend -- getting TURNED AWAY at the door ... all because he was dressed like a lumberjack.

TMZ has learned ... Shaq rolled up to nightclub/restaurant Mars 2112 on Saturday night wearing jeans, a sweatshirt, tennis shoes and a beanie (pictured above with random fan later that night).

But according to the club promoter, Mike Mogul, Shaq's attire wasn't up to club standards ... so security politely informed the retired NBA star that he would not be allowed inside.

Sources at the club tell us Shaq calmly replied, "Are you serious?" ... then shrugged his shoulders and walked down the street to another place that welcomed The Diesel with open arms.

The move is pretty damn shocking, considering TONS of clubs would pay some serious jack to get Shaq to stop by, no matter what he was wearing!!