Perarnau recounts the clash in his new book, 'Pep's Revolution'.
Serialised in the Daily Mail, Perarnau writes: "Pep and Raheem Sterling are having words in the manager's office. Then Sterling's heading out the door with Pep shouting after him, demanding that the player comes back. He isn't finished yet.
"No one else has witnessed their argument and Pep's not sharing: 'It was a private conversation between me and the player.' But they've all heard the raised voices and later piece together what's just happened. Sterling's dropped. He'll be on the bench tonight against Southampton.
"Everyone's taken aback. Guardiola makes a point of never justifying his choice of line-up. To anyone. And now he's done just that with Sterling.
"Today's run-in has been on the cards for a couple of weeks, ever since Sterling demanded an explanation for his absence from a particular team sheet. Now Pep's decided to spell out exactly why the Englishman won't be starting: the team's finishing isn't good enough and, after spending weeks tinkering with his attacking line, this is his solution.
"None of which has gone down well with Sterling, who's stormed out of the office twice, only to be called back in again. Then, after several more furious exchanges, a clearly livid Sterling exits, leaving Pep sitting alone in his office. With the lights out. Simmering with rage.
"It's the kind of call coaches have to make all the time. But Sterling doesn't see it that way. The player seems to consider himself a guaranteed starter and, so I'm told, has also objected to the way Pep's been talking up Kevin De Bruyne and Bernardo Silva.
"The bust-up has affected the whole team. Pre-match, Pep's still furious and he delivers a rambling team talk. Sterling's in attendance but spends the entire game on the bench.
"Fortunately, City win 5-2.
"But Sterling isn't in the squad for City's next game, at Craven Cottage. Pep's clearly taking a strong stand."