Bayern have won just once in five matches since sealing the Bundesliga title in record time last month and a 3-0 home defeat to Borussia Dortmund on Saturday was particularly disappointing.
The club's only win in that run came in the UEFA Champions League, as they progressed to the last four at the expense of Manchester United, but consecutive league defeats to Augsburg and Dortmund have left coach Guardiola anxious.
Guardiola admitted after the loss to Dortmund – in which Bayern's high defensive line was ruthlessly exposed by the pace and movement of their opponents – that he was battling to motivate his side for league matches.
He told Sky Sports: "It happened to me in Barcelona too that, after we had clinched the league title, we really struggled to raise our game again.
"The aim as coach now is to build the team up again. Maybe I made a mistake.
"Maybe it was a mistake not just to carry on as we were, but I don't want to make rotation out to be an excuse.
"I think the problem is we've already won the Bundesliga and we've just dropped off."
Bayern goalkeeper Manuel Neuer went off at half-time in Saturday's convincing loss, but later claimed it was a precautionary move and that he will be fit.
Kosta Runjaic's side have beaten top-flight sides Bayer Leverkusen and Hertha Berlin in their run to the last four, and a 3-2 win at St Pauli on Friday lifted them to fourth in the table.
