The Germany international admits his side "took it easy" after winning the Bundesliga and is determined to repeat their early-season success against Dortmund on Saturday
The Allianz Arena side romped to the title in record time after a blistering first two-thirds of the season, but their struggle for form in recent months culminated in a 5-0 aggregate thrashing by Real Madrid in the Champions League semi-final.
Muller concedes Pep Guardiola's side "took it easy" following their league triumph and has urged his team-mates to finish the season in style with a win in Saturday's DFB-Pokal final against Borussia Dortmund.
"We haven't been on fire for the last couple of weeks, like we were previously. It’s taken a little bit of the gloss off the season," Muller told the official Bayern website.
"The team subconsciously took it easy after winning the title.
"Now we have to let the sun shine through once again. We're ready for the match, where we won’t be expecting any gifts from our opponents.
"It will be like the first Bundesliga game against Dortmund this season [where Bayern won 3-0]. That game had the feeling of a final, because the league hadn't been decided yet."
Saturday's cup final in Berlin is scheduled to kick off at 20:00CET.