Bayern Munich defender Mats Hummels said he could understand fans' frustrations after the club suffered a fifth defeat in six preseason games but added that they had picked the wrong time to boo.
They also lost to both AC and Inter Milan on their tour of China and Singapore and were beaten by Arsenal in a penalty shootout, with their only success coming against Premier League champions Chelsea.
Hummels said the boos "would have been in order" after the Liverpool loss, adding: "We made it far too easy for Liverpool, and it was the worst game that I had ever experienced at Bayern."
But coach Carlo Ancelotti, with the weekend Super Cup clash against Borussia Dortmund in mind, fielded an experimental side, captained by Joshua Kimmich, against Napoli.
Third-choice goalkeeper Christian Fruchtl started, while Sebastian Rudy and Niklas Sule, summer signings from Hoffenheim, made their home debuts.
Hummels, who was on the bench alongside Thomas Muller and Robert Lewandowski for the 90 minutes, said: "Today, looking at who was on the pitch, they [the boos] were badly timed.
"Let's put it this way -- perhaps it's taken them 20 hours and they were still upset after yesterday. We have to accept that.
"Sometimes it's good to get a shot across the bows -- but we've had two or three and that's enough now, otherwise it'll be a really difficult August."
World Cup winning teammate Muller said he "didn't understand" the booing but added that he would "not let it get me down, while CEO Karl-Heinz Rummenigge warned that Bayern "must get our act together."
New sporting director Hasan Salihamidzic said: "We've still got two weeks until the Bundesliga starts, and we will train more intensively.
"Our fans needn't worry because we have a very good squad and coach."