The Foxes are joint bottom of Group C with one point from their opening two games.
They lost 1-0 at Legia Warsaw last month to trail the leaders by five points and are two points adrift of Spartak, leaving Pereira to concede Leicester need a victory on Wednesday.
The right-back said: “Of course, especially having two games with just a draw. It’s important not to wait for the last games. We have to take, normally, 10 points to get to the other phase. We have to start tomorrow. We cannot wait any more.
“Of course, it’s not our first season, a lot of players played in this competition for the first time last year but we are more mature this season. We want to do better and to do that we have to win games. I hope it starts tomorrow.
“In football, in life, we have to always want more. We have to do our best every day, to achieve more and more. We cannot be satisfied with what we did in the past and be OK with that. We have to be ambitious.”
Spartak Moscow are unbeaten in their last four in all competitions – including a 3-2 Europa League win at Napoli – and sit sixth in the Russian Premier League, five points behind leaders Zenit.
Ayoze Perez has not travelled due to illness and Jonny Evans will be assessed after coming off in Saturday’s 4-2 win over Manchester United with cramp having battled a long-standing foot injury.
Boss Brendan Rodgers said: “If we can win the game it puts us in a great position with two home games remaining. If you get to 10 points you will not be too far away from the top of the group.
“One team (Legia) already has six and the other teams have a bit of work to do.
“Momentum is very important and winning after winning is also important. We got back to our level at the weekend and we are looking to bring that similar performance in to tomorrow.
“If we want to continue and go far in the competition this is a game which is going to be really important, especially with two more games to come at home.”