FIFA said it would continue to closely monitor the behaviour of supporters and warned it would not discount taking further action if Mexican supporters repeat the chant during the competition.
In a statement, FIFA said: "The disciplinary committee gave a warning to the FMF (Mexican Football Federation), who may face additional sanctions in case of repeated infringements of this type."
The Serbian Football Association was also fined 10,000 Swiss francs over the appearance of an "offensive and political banner" during the team's opening win over Costa Rica.
Mexico's football federation (FMF) has been repeatedly fined by FIFA over fans chanting the slur.
In the past the FMF has appealed to supporters to refrain from using the chant.
The Court of Arbitration for Sport cancelled two fines against Mexico in November, ruling the chant was "insulting" but not meant to offend, though it left other fines in force.
Mexico topped Group F, along with Sweden, after they beat the 2014 World Champions with a Hirving Lozano goal.
They face South Korea at the Rostov Arena on Saturday.
Source: Skysports