Porto coach Paulo Fonseca admitted his side's hopes of qualifying for the knockout stages of the Champions League are hanging by a thread.
The Portuguese outfit could have taken matters into their own hands by defeating Austria Vienna on Tuesday night but a 1-1 draw means that they will go into the final round of games a point behind second-placed Zenit.
Consequently, Porto will now need to win at unbeaten Atletico Madrid, who have already secured their passage into the last 16, and hope that Zenit fail to triumph in Vienna.
"It's hard for us to enter the last game in this situation," Fonseca lamented after the draw at the Dragao.
"We had the possibility of entering that game depending only on ourselves, but now we have to win in Madrid and wait to see what happens in the other game."
Fonseca felt his side paid the price for a dreadful opening half against their Austrian opponents, with Porto having been able to secure all three points even though Jackson Martinez cancelled out Roman Kienast's first-half opener just after the restart.
"We suffered a goal with 10 minutes played, which unsettled our team," the 40-year-old trainer said.
"We offered the first 45 minutes to our opponents. In the second half we pressured and we created several chances to score.
"But the fact is that we were not able to accomplish our goal, which was to win this game.
"Despite not being at our best in the first half, we reacted well against a team that played with their lines deep in their own half."