European Cup holders Barca defeated Leverkusen 3-1 in the first meeting between the teams on February 14, thanks to Alexis Sanchez's brace and a Lionel Messi goal.
Few observers anticipate any outcome other than Barca progressing to the last eight, but their coach is adamant his players must be wary.
"Recently we have gone into the second legs of the round of 16 after a draw or a defeat," Guardiola said.
"This season we are in a better position than in previous seasons, so I imagine you won't be asking me many questions about the game tomorrow because people think it's done against Leverkusen."
"We dominated Leverkusen in the first half but they were very strong in the second half, and very fast."
"This competition is very tough and to reach the quarter-finals would be great because this tournament is so good."
"Leverkusen never give up a match as being lost, never give up. It looks like they're dead and suddenly they hit back."
"I hope we have 70 percent of possession, I really do."
Leverkusen were level at 1-1 in the first leg thanks to a goal from Michal Kadlec, while the likes of Andre Schuerrle and Stefan Kiessling are also equipped to threaten La Liga champions Barca.
"What concerns me is their speed," Guardiola said.
"They (Leverkusen) have their chances of qualifying, of course they do - Bayer want to be at the top again."
"We have to control the match and make sure they don't pick up speed."
source : soccerway.com