The ringside doctor SHOULD HAVE stopped the Tyson Fury fight based on the size of his gash ... but they let it go because Tyson is a huge star -- so says Otto Wallin.
The Swedish fighter tells TMZ Sports ... if the tables were turned, the doctor would DEFINITELY have called the fight because the wound was massive and posed a real medical danger.
"If it was someone else, they probably would have stopped it," Wallin said while hanging at a Vegas pool party.
Still, Wallin is being praised for his gutsy performance .