Rudiger reacted to something Cabral said to him during an exchange of words in stoppage time of Madrid's 3-1 win by raising a complaint to Brazilian referee Ramon Abatti Abel.
The bizarre interaction occurred at the Oval Office - with FIFA president Gianni Infantino also present - and no explanation has been given as to why the gathering took place.
The competition has drawn widespread criticism so far, with FIFA struggling to fill stadiums and players playing weeks after some of their domestic seasons had come to a close.
Chelsea's opening match against Los Angeles FC, played at the Mercedes-Benz Stadium in Atlanta, Georgia, was more than three-quarters empty with just 22,000 fans inside the 75,000-capacity venue.
FIFA's rebranded Club World Cup got underway in the United States on Saturday night - but some fans were less interested in the football and more baffled by a bizarre new award name.
RIATH AL-SAMARRAI: There are some nice angles to FIFA's Club World Cup . Here's one: Auckland City. Here's another: their goalkeeper. That would be a guy named Conor Tracey.