Coach Luiz Felipe Scolari said Portugal faced a "life or death" match against Russia after the 2-1 defeat by Greece.
"In a short competition of only three games, the first game is vital. The next game is crucial for us. The next game is life or death," said Scolari.
"I'm beaten down and sad. But these results happen. You work for a victory and then you lose. The players are really depressed and myself too.
"We lost control," Scolari added, whose team also face fancied Spain.
"I want to apologise for the result and our performance
which didn't reward the backing we had from the public," said the Brazilian.
"We created a few chances but Greece were well organised,
they closed up at the back and exploited the counter-attack."
Portugal midfielder Luis Figo insisted the hosts can bounce back from defeat.
Real Madrid star Figo said: "We have two more games to play, so let's see what happens in those.
"We didn't deserve to lose this game, Greece created two chances and scored two goals.
"But when you play at the highest level and make mistakes like we did for the goals, and give the ball away in midfield, you will get punished."
Figo added: "The game started really difficult for us with the early goal.
"We tried to score but it was difficult in the second half with the penalty.
"We're all disappointed but it's a big disappointment for the supporters."