UEFA’s William Gaillard told The Sun: “We won’t tolerate racism. We have had many problems with this in Eastern Europe before and Croatia have been among the worst offenders.
“But we are determined this will not happen again and will send out a strong message to stop any incidents during the game against England.
“FIFA have recently introduced new rules which can, in extreme cases, lead to a team being docked points or even being excluded from the competition.
“Because of the problems we have encountered with Croatian teams in the past, they have been warned future sanctions will be much heavier than any which have been imposed for previous incidents.”