Coach Zlatko Dalic said he "apologised" to the tens of thousands of Croatia fans who travelled for his side's disappointing opening 3-0 loss to Spain at Euro 2024 in Berlin on Saturday.
Croatia were stunned by a vibrant first-half display from Spain as goals in the opening 45 minutes from Alvaro Morata, Fabian Ruiz and Dani Carvajal left Dalic's men precariously placed in Group B.
They are attempting to reach the knockout phase at a fifth consecutive major tournament, after finishing third at the Qatar World Cup two years ago.
"It was a great atmosphere. I don't know how many Croatia supporters were here today," he said of the crowd at the Olympiastadion, which was vastly made up of Croatia fans.
"I apologise for this bad show today... It was amazing how many of them travelled here and my message is that I apologise to them...
"We weren't aggressive enough, we were too far away from their players. We gave them too much space and when you give such players so much space, it is difficult. Especially in the first half."
Croatia next face Albania in Hamburg on Wednesday, before a potentially crucial closing group match against reigning European champions Italy in Leipzig on June 24.
Manchester City's Josko Gvardiol played at left-back rather than in central defence, but Dalic insisted he would not be pressured into a change despite being angered by the manner of Morata's 29th-minute opening goal.
"That deep, vertical ball we have spoken about," Dalic said of Ruiz's through ball from inside his own half which set Morata away.
"It was a cheap goal... We had a lot of issues in that part of the defence but until now it has been good so I hope this was just a bad day.
"We won't erase everything we've done well, there were good games before when he (Gvardiol) played in that position.
"We have two matches left to get through the group and this was a bad day. We need to see why it was bad and what we can do."
Dalic withdrew key midfielders Luka Modric and Mateo Kovacic in the 65th minute, but said that was just to ensure they are ready for the coming games.
"They played for an hour and we realised we have two difficult matches in front of us against Albania and Italy and we didn't want to force them to play until the end... so we decided to rest them."