Koller's men qualified with a flourish, winning nine games out of 10 on the road to France, but they were brought to a halt by unfancied local rivals Hungary, who claimed an opening 2-0 win in Group F on Tuesday.
To make matters worse, playmaker Zlatko Junuzovic sustained an ankle injury to join suspended defender Aleksandar Dragovic on the sidelines.
Nevertheless, Koller believes his players are in good spirits ahead of the daunting prospect of tackling Cristiano Ronaldo on his record-breaking 128th appearance for Portugal.
"Of course we have to play different to how we played against Hungary," the 55-year-old Swiss told his pre-match news conference in Paris.
"We have analysed the game. We have tried to motivate our players. Their morale is upright again.
"We have to do three things - to use our chances, play more calmly and be more compact defensively.
"We were not compact enough in the last game and we committed mistakes Hungary could benefit from."
Koller conceded he had been hard at work making sure his players were in the right frame of mind for a return to action four days on from their loss to Hungary, but insisted this is an area of preparation he likes to stay fully on top of.
"It's not only when you lose a game that you should be able to deal with pressure well," he explained.
"You should talk to players if you perceive that they suffer from pressure. We are all occupied by this in the management team.
"We are trying to motivate them again to show them the right way and show them there are several things that we've done well.
"If you succeed in doing them better than the opposition you will succeed and will win the game."