The Spaniard's three-year contract expires next June and Bayern's head coach has said he will announce "before Christmas" whether he will extend his stay or leave, with Manchester City among the English sides keen to secure his services.
According to German daily Bild, Guardiola gave his decision to Bayern boss Karl-Heinz Rummenigge "last week".
"Everything points to his leaving," the paper added.
Kicker suggested his departure was "an open secret".
The 44-year-old Catalan is in his third year at the helm of the Bavarian giants.
Last month Rummenigge indicated that talks on his future would begin after December 19 "to avoid any Christmas surprise, one way or the other".
Barcelona daily Sport claimed a month ago that Guardiola had already given his word to former Barca colleagues Ferran Soriano and Txiki Begiristain, now Manchester City's chief executive and director of football respectively, that he would join them at the Etihad next season.
Bild suggested Guardiola was alive to the danger of out-staying his welcome if he remained at Bayern.
"He is someone who enjoys a challenge. That's the reason why he joined Bayern in 2013," the paper said.
Bayern laboured to a 1-0 German Cup win over Darmstadt on Tuesday to book their place in the quarter-finals and keep alive their dreams of winning the treble of Champions League, Bundesliga and cup titles this season.
The Bavarian giants hold a five-point lead in the German league ahead of their final game of 2015 at Hanover 96 on Saturday, but the sense of anticipation is building in the Bayern squad over Guardiola's impending announcement.