Guardiola was feeling the frustration early into the season after a 1-1 draw with Everton at the Etihad Stadium.
City had dominated but had been unable to make their superiority count - a failing familiar from the previous campaign.
Guardiola locked himself in his office, but a knock on the door and a message of support proved just what the City boss needed - and it inspired a record run of 18 straight Premier League victories that would go a huge way towards securing the title that season.
“That evening was a tense and difficult moment but it would spawn thousands of wonderful ones," Khaldoon says in the book, 'Pep's City — the Making of a Superteam', according to The Sun.
"When you set out to do something so difficult and ambitious, the joy and stress go hand in hand."
City's director of football Txiki Begiristain knows that moment on a tense and anxious day was crucial.
He said: “It was the way Khaldoon talked to him that night, he showed how much confidence he had in us.
“It had been a dreadful day. We'd been the better team but hadn't got the result and everyone was feeling a little bit shaken.
“Khaldoon told Pep that he knew it wasn't easy, but he had complete faith in what he was doing.
“He said that in his eyes there was no other way for the club to proceed. Only his way — the Guardiola way.
“Was it what Pep needed to hear? Of course. But he said it with such conviction and Pep believed him."