Hugo Lloris saved Tottenham against Leicester, but the captain knows he will not be able to repeat the feat if his side defend the same against Borussia Dortmund in the Champions League on Wednesday.
The France international kept out Jamie Vardy's penalty, which was the striker's first touch of the game, and made a number of other important stops as Spurs won 3-1 at Wembley.
Although the scoreline suggests an easy win for Mauricio Pochettino, Leicester were well in the game and had 20 shots at goal.
Lloris was able to bail his side out, but the prospect of conceding so many chances against the Bundesliga leaders in the first leg of their last-16 Champions League tie worries him.
"Leicester played in a fantastic way and I think we won the game thanks to our spirit and character," Lloris said. "Without that, we could not win this game.
"I think we need to improve the team performance. We won but against a bigger side we couldn't have won that type of game. It's up to us.
"Against a bigger side it would be even more difficult to win. It's the way you manage the season too, though. Sometimes you deserve to win, like the game against Man United, and you lost.
"Leicester deserved better but we won. This is the league. It's a long way and without spirit and character, it's difficult.
"The mentality is great in the changing room and we showed that again on a difficult day."