Preview: Barca wary of Bayern backlash
"League form has nothing to do with the Champions League, but in my opinion it is the worst possible result for us," Guardiola said.
"Bayern have won the European Cup four times and have won their domestic league many times, and it is now sure they will arrive with even greater motivation," he told reporters.
The Primera Liga leaders resumed their push for honours on three fronts with a gritty 1-0 win at Real Valladolid on Saturday, when Guardiola got away with resting Thierry Henry, and using Lionel Messi and Daniel Alves as substitutes.
The Catalans, who have already reached the King's Cup final, maintained a six-point lead over chasing Real Madrid with nine games left.
"After the break for internationals the win over Valladolid was vital to get our competitive edge back," Guardiola said.
"The players gave their all and the shouts of happiness you could hear from the dressing room afterwards show how important we felt the three points were."
Guardiola has a doubt over the fitness of midfielder Yaya Toure who is due to return after a thigh muscle tear but captain Carles Puyol and midfielder Andres Iniesta are fit again after injury layoffs.
Bayern coach Jurgen Klinsmann has recovered Hamit Altintop from injury while striker Luca Toni played for the first time in the 5-1 defeat at VfL Wolfsburg on Saturday after more than four weeks out with a heel injury.
But the Germans, who defend an undefeated run in the Champions League this season, will be without striker Miroslav Klose, out for several more weeks after surgery, and central defender Lucio, who sustained a thigh injury on Saturday.
"We are not afraid of Barcelona," said Klinsmann. "The players know that the whole world will be watching and they will want to show what they can do."
But he demanded greater commitment following the defeat against Wolfsburg.
"The players must know that there will be consequences at some point," he told the club website (www.fcbayern.de).
He said he wanted to see "greater sacrifice and determination."
Barcelona: 1-Victor Valdes; 20-Daniel Alves, 4-Rafael Marquez, 3-Gerard Pique, 5-Carles Puyol; 6-Xavi, 15-Seydou Keita, 8-Andres Iniesta; 10-Lionel Messi, 9-Samuel Eto'o, 14-Thierry Henry
Bayern Munich: 1-Michael Rensing; 23-Massimo Oddo, 6-Martin Demichelis, 5-Daniel van Buyten, 21-Philipp Lahm; 31-Bastian Schweinsteiger, 15-Ze Roberto, 17-Mark van Bommel, 7-Franck Ribery; 9-Luca Toni, 11-Lukas Podolski
Referee: Howard Webb (England)