After another weekend break, we face Steve Bruce's side at the Lane in a match we have to win to get back on the European trail in the Premiership.
Three successive defeats have seen us slip down to tenth in the table but the lads are determined to turn it around against a Birmingham side that should include their former team-mate Steve Clemence.
Gus remains optimistic that we can turn it around but conceded: "We can have no more mistakes.
"I said last week was a vital game and now it is this one.
"The next game is always the most important but now there is no more time, it has to be now.
"We have to win a few games if we are to have a chance of Europe because it is getting harder now.
"I'm optimistic that we can have a good run at the end of the season, when everyone else a little tired and boom, you can win a few games and find yourself in a good position again.
"The problem is, after the last three games, we can't afford to lose. This is a chance for us but we have to go and prove it on the pitch.
"This game will be hard but every game is hard now. Everyone is fighting for something but it is up to us to play our game."
Gus Poyet says there can be no more mistakes from now until the end of the season - starting against Birmingham City on Saturday.