"It is very difficult to know what the offside rule actually is - there is too much open to interpretation now," Hughes said after the 1-0 defeat.
"Djibril Cisse made a movement towards the ball, he was stood in an offside position and the linesman on the far side was not in a position to know whether he touched the ball or not.
"It will be very difficult to get that Champions League spot now. We are running out of games and the sides above us are in better shape, but we've just got to make sure now that we get three points on Wednesday night (at Birmingham)."