Croatia's football federation was fined 6,600 euros by UEFA for failing to comply with doping procedures, though Olic was cleared to keep playing after using a pain-killer for a rib injury suffered in a pre-tournament friendly.
Team doctor Zoran Bahtijarevic told Reuters that Croatian doctors should have signalled the use of the pain-killer before Olic took a dope test after Thursday's 2-2 Group B draw with France.
"This we failed to do...that was basically our mistake," Bahtijarevic said. "There was no intention of doing anything illegal, it was an administrative mistake, as you can see by the very mild disciplinary measures from UEFA.
"It was definitely embarrassing for our medical team because it was clearly our failure and we took responsibility on ourselves completely."
However, Bahtijarevic said the squad's preparations for Monday's final group game with England had not been compromised by the affair.
"The team was not disturbed because we knew that Mr. Olic was not guilty of any violation," he said.
That view was backed up by Croatia midfielder Milan Rapaic, who told Reuters: "We knew there was nothing in it. It was just routine treatment.
"The team are concentrated on the game tomorrow, it's all we are thinking about. It's a hugely important one for us because after 90 minutes we're either going home or staying in the tournament."
Croneed a win atia to go through to the quarter-finals, while a draw would be enough for England.
