Carlos Queiroz's side went into the Group 1 campaign as favourites to secure the automatic spot for next summer's World Cup finals in South Africa but instead find themselves on the verge of elimination.
With two games left, Portugal trail leaders Denmark by five points and Sweden by two, with the Scandinavian rivals facing each other tomorrow in a blockbuster encounter.
Hungary are level with Portugal on 13 points after eight games and the losers at the Estadio da Luz tomorrow will almost certainly find themselves out of contention for even a play-off spot.
Indeed, a Sweden victory and a draw in Lisbon would rule both teams out and, with the Copenhagen clash kicking off an hour and three quarters ahead of Portugal's match, the scenario will be clear for Queiroz's men.
Carvalho told www.fpf.pt: "We have to take the chances we create, knowing Hungary also have more to gain than to lose. They have to attack because they still have possibilities."
Regarding the difference in the kick-off times, the Chelsea defender added: "We preferred to play at the same time but, either way, we have to win our game and beat Malta on Wednesday."
With both games at home, Portugal should have a good chance of salvaging at least a play-off place but they have yet to win on home soil this campaign, with goalless draws against Albania and Sweden and a 3-2 defeat by Denmark.
Scoring goals has been their major downfall, with FIFA World Player of the Year Cristiano Ronaldo failing to match his club form at Manchester United and Real Madrid.
The £80million man has not found the net at all this campaign but his fitness following an ankle problem will still be a boost for Queiroz, while full-back Jose Bosingwa is also expected to play.
Striker Nuno Gomes is still hopeful Portugal, who finished fourth at the last World Cup in Germany, will qualify.
"I'm confident in these two games to guarantee at least the play-off spot, and later guaranteeing a place at the finals through that route," he said.
"For me personally, to be at another World Cup finals would be a source of great pride."
Sweden coach Lars Lagerback has his sights firmly set on three points in Copenhagen, with Denmark having stuttered slightly, drawing their last two matches.
Lagerback, who should have striker Johan Elmander available after injury, said: "We've talked a lot about going in and taking the initiative and not being afraid to play our game.
"You have to tap into the attitude of the players and there should be no problem with it. The focus is to win the match, the most important thing is three points."
Denmark can secure top spot with victory over Sweden but their hopes have been dealt a blow by the news Jesper Gronkjaer is out because of ongoing knee problems.
Coach Morten Olsen, who has called up Johan Absalonsen in his place, told www.dbu.dk: "It is obviously a very bad situation for us when we think about the importance of the forthcoming games.
"Jesper has the experience and quality, which can be crucial to our chances in those matches. But we have respect for Jesper's sense of his own situation."