Guardiola confirmed the midfielder wasn't able to recover in time from an ankle injury for the trip to Leverkusen on Wednesday. Bayern is still without the midfielder and other key players.
Bastian Schweinsteiger will miss Bayern Munich's German Cup quarterfinal at Bayer Leverkusen after suffering an ankle injury in the 1-0 win over Borussia Dortmund on Saturday.
The 31-year-old was substituted on 58 minutes at the weekend having suffered a knock on his ankle in the first-half. But tests, and a trip to the club doctor on Monday, ruled out serious damage to his bruised left-ankle.
The Germany captain is the latest to head for the treatment room at Säbener Strasse amid an injury crisis that leaves Arjen Robben, David Alaba, Franck Ribery and Javi Martinez unavailable for selection.
"He's definitely out," confirmed Pep Guardiola. "We're lucky that Philipp Lahm is back again."
When asked whether his normal style of play would be compromised by the number of injuries in his squad, he added: "It doesn't matter, there are no excuses.
"We have 16 fit players and also young players for whom playing against Leverkusen is a great experience. We must win. If not, then there are handshakes with the Leverkusen coach and we move on."
April will be a season-defining month for Bayern Munich who holds a 10-point lead at the top of the Bundesliga with a double-header to come against FC Porto in the Champions League.
Bayern has already lost two matches in 2015 to sides in the top-four and despite winning at Borussia Dortmund, Guardiola has demanded an improvement from his team ahead of the crucial period.
"Recently we've played some good games in the league and Champions League," he said.
"But against Dortmund we didn't play well. We need heart and passion - that's football, lots of running and fighting.
· Schweinsteiger and Ribery are injured. The latter could still miss the Porto clash.
· Lahm isn't in the best condition.
· Jerome Boateng is a top, top, top, top player.
· Great admiration for Leverkusen.
· Wary of Leverkusen's strength via Kiessling, but also positive words for Castro.
· Praise for Lewandowski's performance in Dortmund.
· Penalty shootouts are about mentality. So no practice.