It’s certainly nothing to do with the form of the player, it’s just that the Spaniard is concerned that the Brazilian will pick up a yellow card and be forced to serve a two-match suspension. Should this happen he wouldn’t be available for the trips to Fulham and Liverpool.
Although the 25-year-old is just one booking away from the two-match suspension for receiving 10 yellow cards at this stage of the season, that particular punishment will expire after this weekend’s matches and he would no longer be at risk from the Fulham game onwards.
Luiz has been Benitez’s first choice defender since the former Inter and Valencia manager took charge, and he’s probably one of the most improved players in the squad during that time. John Terry will likely step in for Luiz should he be omitted from the starting line-up against Manchester City to play alongside Branislav Ivanovic, who has improved his form of late.