Brendan Rodgers's side trail 2-0 going into the second leg of the tie after succumbing to defeat at the Petrovsky Stadium.
"It will be the biggest European game I've ever played in. We know we have to score at least two, but we can do it," Enrique told The Mirror.
"It's so important to keep a clean sheet against Zenit. They spent a lot of money so they have good players, but we have to stop them scoring. We need to concentrate throughout."
The winner of the match will play either Basel or Dnipro in the last 16 of the competition.