Midfielder Sean Thornton will serve a four-match ban after the Football Association rejected Leyton Orient's appeal for wrongful dismissal.
Thornton, 24, was given a straight red in the first half of Saturday's match against Leeds at Elland Road for
allegedly punching winger Seb Carole.
The FA stood by referee Nigel Miller's decision that Thornton "punched the opponent in the head."
Thornton will miss games against Port Vale, Doncaster, Oldham and Swindon.