An opening day draw against co-hosts Poland followed by a 2-1 defeat to the Czech Republic have left the Euro 2004 winners’ quarter-final hopes hanging by a thread.
Anything less than a win against Fernando Santos’ side will see Greece crash out, with their opponents needing just a point.
"Tomorrow's game is the most important one we have played in the past two years,” Papastathopoulos told reporters. “We all want to win.
"There are no outsiders or favorites for tomorrow's match [against Russia]. It's just 90 minutes.
"It's very important that a 1-0 win van be enough for us to go through."
Veteran striker Fanis Gekas told the assembled press that Greece must believe in themselves on Saturday against the Group A leaders.
"If we are focused and self-confident, we can make it against Russia.
"The draw between Russia and Poland was the best possible result for us. We have pressure for the win, but Russia have also pressure not to lose the game."
Reacting to criticism following the loss to the Czechs, Santos spoke at length about how Greece have analysed Russia’s style.
Like Gekas, he also highlighted the importance of self-confidence and still retains hope that they can progress to the quarter-finals despite occupying last place in the group.
"We know very well Russia's style of play,” he added. “We have exhaustively analysed it. I know that is being said that we weren't prepared against Poland and Czech Republic, but that's not true.
"Russia's two strong points are their through balls and their passing game. But they are also very good in counter-attacks. We need to be focused in our game and look with self-confidence for the goal that will lead us through to the next stage.
"We must be more aggressive in our defensive game. We must not let the Russians go first to the ball."