Mexico fans have long shouted an insult that gay rights groups argue is homophobic at keepers taking goal kicks.
"Further updates will be communicated in due course," said FIFA. "As proceedings are ongoing please understand we cannot comment further at this stage."
The Mexican football federation (FMF), which has repeatedly appealed to fans to stop the chant, was sanctioned 12 times for homophobic chanting during the World Cup qualifying campaign, receiving warnings for the first two offences and fines for 10 more.
The chant was widely heard at Mexico games in the 2014 World Cup in Brazil, when FIFA took no action, but it has since launched a clampdown and other Latin American teams, including Argentina and Chile, have also been fined.
FIFA is employing three specialist observers at each World Cup match to report discriminatory behaviour by spectators.
