After four matches in Group F, the reigning European champions are second behind Borussia Dortmund, with a five-point cushion to Tuesday's opponents.
Zidane does not see it that way, though, and he is expecting to leave the Portuguese capital with all three points.
"Winning against Atletico means nothing for tomorrow, we have to start well and if we do that we can get something here," he told a pre-match media conference.
"But I'm expecting a very difficult game tomorrow.
"I'm not thinking about first or second place, I am thinking about the players, the club, the team and always doing everything to win the game, nothing more.
"Whatever happens [after that] then we'll look at the qualifying but most important thing is what we are going to do tomorrow, we'll do everything possible to win.
"I am not going to calculate anything, and the same for the players."
Zidane will decide whether Karim Benzema and Sergio Ramos are fit to participate prior to kick-off but both have travelled to Lisbon with the squad.
And both could be used ahead of what Zidane anticipates being another tough challenge – the first meeting in the group having been decided by two late Madrid goals at Santiago Bernabeu.
"They [Sporting] have not surprised us," the Frenchman added. "They played really well [in Madrid], we won with difficulty.
"Tomorrow we will have a similar game against a team who will want to cause us problems.
"They'll come out and it'll be a great game. When people play against Real Madrid they give more or try more, it's normal, it's logical that when play Real Madrid, you play better.
"Tomorrow we have to hope they don't play as well."