Croatia have fitness worries about three key players ahead of the World Cup finals.

Zlatko Kranjcar's men face a tough task if they are to progress to the knockout stages in Germany after being drawn in Group F alongside Australia, Brazil and Japan.

That task could be made much harder if captain Niko Kovac, defender Josip Simunic and goalkeeper Tomislav Butina fail to recover from injury in time to play in Croatia's opening game against holders Brazil in Berlin on June 13.

Kovac suffered a thigh injury during last weekend's 2-2 draw against Iran and has been ordered to rest for the next few days.

He is unlikely to be risked in Saturday's warm-up match against Poland, but Simunic and Butina could get a chance to test their fitness after making progress in their recovery from respective knee and foot problems.