The Premier League leaders were controversially eliminated from the Champions League on Wednesday, after losing 3-2 on aggregate to La Liga champions Real Madrid.
The defeat was United's first since December, and Luiz is now hoping that the Blues can inflict back-to-back defeats on the Red Devils and dump them out of another competition.
"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 told Sky Sports News.
"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."
Chelsea travel to Old Trafford for their FA Cup quarter-final clash with United on Sunday.