The Brentford manager confirmed that the Brazilian went into the Bees' dressing room after the game to say sorry for the late challenge that left Jake Reeves with a concussion.
Rafa Benitez's team was ahead by four goals and in complete control of the game when the Brazilian charged into Reeves with his shoulder after the ball had been played. Rosler praised Luiz's "fantastic gesture" after he visited the Brentford dressing room to make amends.
"Jake is fine," Rosler told reporters. "He wanted to continue but our medical staff said it’s better not to. Safety first, but he will be OK next week. He was definitely concussed.
"I haven't seen the Luiz challenge clearly enough to make a judgment. He came into our dressing room afterwards to speak to Jake, and I think that's a fantastic gesture."
Chelsea will face Middlesbrough in the fifth round and will learn its potential quarterfinal opponent when the draw is conducted later on Sunday.