The Bavarians kicked off their 2014-15 campaign with a DFL-Supercup showdown with Borussia Dortmund on Wednesday evening but goals from Henrikh Mkhitaryan and Pierre-Emerick Aubameyang saw Jurgen Klopp's men defeat the reigning German champions in the season-opener for the second year in a row.
Guardiola's starting line-up was devoid of a number of World Cup stars, including Germany's Bastian Schweinsteiger, Philipp Lahm and Mario Gotze, but the Catalan accepted his team had performed poorly at Signal Iduna Park and that they need to improve quickly ahead of their first Bundesliga fixture, against Wolfsburg on August 22.
"We played well in the first 15 minutes but then we had a number of problems," the Bayen boss told reporters. "In the second half we retreated too.
"We still need more time to prepare. We tried to play well but we had problems controlling the game. We have to train a lot still."
Ahead of the game, the former Barcelona boss had claimed that he only had eight or nine fully fit players for the pre-Bundesliga season clash with BVB.
A major injury to defensive midfielder Javi Martinez in the Supercup defeat Bayern may now see the coach without one of his key players for much of 2014-15, if initial reports of ligament damage are confirmed.