Manchester United boss Sir Alex Ferguson said: “Louis thought he heard a whistle.
“Louis is obviously disappointed to miss the penalty but the players will help to lift him because we are all together at this club.
“There are no problems with the boy. I am sure he will miss another penalty in his career at some point.
“Understandably, the players are disappointed. We have five days to lift them but if we want to win the league we have to show character and I am sure we will.”