Uefa has warned Croatia they could be kicked out of Euro 2008 if fans direct any racism towards England's players.
Fifa charged the Croatian Football Federation with bringing the game into disrepute after fans formed a human swastika during a friendly in Italy.
Ahead of Wednesday's Euro 2008 qualifier in Zagreb, Uefa spokesman William Gaillard said: "We can impose heavier sanctions if it happens again.
"That ultimately could be exclusion from the competition."
England's black players have been subjected to racist abuse in the past, with Ashley Cole being targeted by Spain fans in a friendly in Madrid.
Uefa has contacted the Croatian government to spell out their warning, while their football federation has also implemented measures to ensure there are no problems against England.
Croatia are keen the match goes ahead without incident because they are making a joint bid with Hungary to host the 2012 European Championship.
The disrepute charge from Fifa followed the swastika incident, which involved 200 supporters at a friendly against Italy in Livorno in August.
Croatia were fined during Euro 2004 over racist banners flown at a game against France.
Gaillard added: "There are new rules, which can lead to exclusion from a competition and docking points in extreme cases. We will monitor events closely.
"Ourselves and Fifa have imposed sanctions and the sanctions will be heavier in the future."