Striker Ivica Olic is out of Croatia's Euro 2012 squad with a ruptured thigh muscle and has been replaced by Nikola Kalinic, team officials said on Monday.
Olic picked up the injury in Saturday's 1-1 draw against Norway in Croatia's final warm-up ahead of the June 8-July 1 tournament in Poland and Ukraine, where they have been drawn in Group C alongside holders Spain, Italy and Ireland.
"Unfortunately, the injury turned out to be far more serious than the initial examination had suggested and a thorough scan showed a rupture in the right thigh," team doctor Zoran Bajtijarevic told Croatian media.
"It came as a shock to everybody, including Olic, because his subjective impression matched initial predictions that it wasn't serious but he will now need up to six weeks to recover."
The Croatians open their campaign against the Irish in Poznan on Sunday.
Coach Slaven Bilic had earlier named Kalinic as a first-choice reserve if any of his forwards suffered an injury and the former Blackburn Rovers striker should have litte trouble fitting in after scoring in Croatia's 3-1 friendly win over Estonia on May 25.