Bayern Munich's pre-season came to a close in disappointing fashion as it lost 2-0 to Napoli in the Audi Cup third-place play-off.

Goals from Kalidou Koulibaly and Emanuele Giaccherini gave Maurizio Sarri's side all three points and compounded Bayern's miserable run of form ahead of the start of the 2017-2018 season.

Head coach Carlo Ancelotti rested a number of senior players in the wake of the 3-0 loss to Liverpool on Wednesday (AEST), handing a start to several youngsters including Timothy Tillman and Manuel Wintzheimer.

Napoli, which lost 2-1 to Atletico Madrid in its semi-final, kept faith with a strong line-up and was good value for the lead given to it by centre-back Koulibaly.

Giaccherini's well-taken finish made the win safe for Sarri's men as Bayern struggled once more to make the most of consistent spells of possession, leaving it with five defeats from its past six pre-season games and a stark lack of confidence ahead of the DFL-Supercup clash with Borussia Dortmund on Sunday (AEST).

Jose Callejon threatened a shaky-looking Bayern defence before Koulibaly broke the deadlock from a corner, blasting into the net after Christian Fruchtl's parry bounced off the head of the prostrate Arturo Vidal and into his path.

Fruchtl denied Dries Mertens one-on-one as Napoli threatened to seize control of the match, however Luigi Sepe had to react smartly to deny Wintzheimer from close range.

Arturo Vidal saw the funny side when he fluffed a shot behind for a goal-kick, but Bayern was again struggling to turn possession into meaningful chances, although Tillman forced substitute Rafael into a low stop just after the break.

Any hopes of rescuing a result suffered a mortal blow after 55 minutes when Giaccherini was given time and space to collect Callejon's cross and rifle into the bottom-left corner from 12 yards out.

Mertens hit the side netting when played clean through moments later, but Napoli was largely untroubled in the closing stages of its fourth pre-season victory to date.