Holders Barca have occasionally slipped up against what Guardiola called the "small teams" prompting accusations of complacency, and the last time they lost in Europe's elite club competition at the Nou Camp was to unfancied Rubin Kazan of Russia almost exactly two years ago.
Since that 2-1 reverse they have won nine and drawn two at their massive arena in the Catalan capital but Guardiola, a former Barca midfielder who has won two continental titles in his first three seasons as coach, told a news conference on Tuesday he was not taking anything for granted.
"Typically these kinds of teams are underestimated because you don't see them playing and you don't know them," the 40-year-old said.
"Losing respect for Viktoria Plzen would be a great mistake," he added.
"We have always had more trouble with small teams than with the more prestigious ones."
Despite Guardiola's concerns, the sparkling form his gifted squad has shown this season suggests anything other than a convincing victory for the home side would be a massive shock.
They are unbeaten in 18 matches in all competitions stretching back to a La Liga defeat at Real Sociedad in April and have scored 40 goals in their opening 12 games this season, 15 more than in the same span of matches last term.
Their Argentine World Player of the Year Lionel Messi, Champions League top scorer the past three seasons, has continued his astonishing run of breathtaking goals and has two in two games in Europe and 10 in seven matches in La Liga.
Messi told an earlier news conference on Tuesday there was little danger he and his team mates would lack motivation against the Czech champions on Wednesday.
"We are always motivated in the same way," the 24-year-old said, praising Guardiola for his coaching methods.
"He is always looking for new details, new ways to improve at every training session, every day," Messi said.
"In the Champions League there are no easy teams, wherever they come from.
"They [Plzen] played a good game against AC Milan and had chances to score.
"We will play the same way as ever, respecting the opponent and trying to play our game and having as much possession as possible."
Barca are level with Milan on four points from two games, with Plzen and BATE Borisov of Belarus on one point.
