United were beaten 2-1 by Real Madrid on Tuesday night after Nani was controversially sent off at Old Trafford as Los Blancos progressed to the quarter-finals.
But Luiz claims that United’s confidence will have been dented by Tuesday’s loss ahead of Chelsea’s quarter-final showdown with Ferguson’s men at Old Trafford on Sunday.
“It’s difficult when you have been knocked out of an amazing competition like the Champions League because your confidence is not the same after,” Luiz said.
“The happiness in Manchester United’s hearts will not be there and Chelsea can use this to win our game on Sunday.
“United will be playing at home but some players and supporters will be thinking ‘it’s not the Champions League’ and it will be difficult for them to come in with the same form.”