Zlatan Ibrahimovic’s ghostwriter has admitted he was not quoting the Paris St Germain striker in large sections of his autobiography I Am Zlatan.

David Lagercrantz, speaking at the Hay Festival, said that rather than faithfully documenting Ibrahimovic’s thoughts, he simply invented many of the quotes in the book.

“I worked with Ibrahimovic very thoroughly,” said Lagercrantz, as quoted by the Daily Telegraph. “I just asked him about things I didn’t know … I think it really was his true voice. The key thing is that I was not working as a journalist. I was not quoting him. I know this – if you want to find something that sounds true and authentic, the last thing you want to do is quote. I don’t think I have any real quotes from him. I tried to get an illusion of him, to try and find the story. I tried to find the literary Ibrahimovic.”

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The book was on the shortlist for the 2013 William Hill sports book of the year. The Guardian’s Richard Williams described it as “what might well be the most compelling autobiography ever to appear under a footballer’s name”. Full of forceful assessments, the book says of the volatile Italian defender Marco Materazzi: “He’s like me. Hatred and revenge are what gets him going,” while Pep Guardiola is criticised for his demands that players conform: “A proper manager can deal with different personalities.”

The player’s fellow Swede Lagercrantz admitted to some nerves when the time came to turn in his work. “You can imagine the moment when I, the fake Zlatan Ibrahimovic, had to send the manuscript to the real Zlatan Ibrahimovic,” he said. “The first thing [Ibrahimovic] said was: ‘What the fuck is this? I never said this!’ But after a while I think he understood what I was trying to do. Nowadays he thinks it’s really his story.”