Paulo Bento's men must realistically win both their remaining matches against Israel and at home to Luxembourg on Tuesday, then hope leaders Russia slip up against lesser teams.
With Fabio Capello's men ending their campaign with away games in Luxembourg on Friday and the group's bottom side Azerbaijan on Tuesday night, Almeida accepts Portugal's chances are slight.
But Almeida, who is favourite to replace the suspended Helder Postiga, said: "We have to worry about this game and the next game and just concentrate on ourselves.
"We know Russia have easier games but you never know. We just have to win. We know the strengths of our opponent and how we suffered in Israel, and it is only in our heads to win."
Israel need a similar miracle if they are to reach a play-off spot, needing to beat Portugal on Friday and also win their last match while hoping Portugal slip up at home to Luxembourg.
The remaining fixtures cast perennial minnows Luxembourg in a pivotal role in the group and it could not come at a better time for Luc Holtz's men after recording only their fourth World Cup win in their history over Northern Ireland last month.
And veteran midfielder Rene Peters insists there is no chance of Capello's Russia taking his side lightly as they look to secure their place in another World Cup finals.
Peters said: "I'm sure Russia will not underestimate us. We know our chances are small, but one day it can only be possible if we believe that we can surprise the favourites.
"It's funny when people ask what chance we have against Russia or other major teams. It is a sign we have evolved and improved because before no-one dared to ask the question because they knew it was going to be a rout."
Meanwhile Northern Ireland will look to put the embarrassment of their defeat to Luxembourg behind them when they travel to Baku to take on Azerbaijan.
Michael O'Neill's side are desperate to restore confidence but they will come up against determined opponents with former Germany coach Berti Vogts hoping to end his reign as Azeri national coach on a high.