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The 38-year-old announced that he would be leaving Los Angeles Galaxy after they crashed out of this year's MLS Playoffs, ending an 18-month spell in the US that saw the Swede score 52 goals in 53 games.
Ibrahimovic has since been linked with numerous sides from around the world, including Australian A-League outfit Perth Glory and Manchester United.
However, Graber has indicated to ESPN that the Swede has chosen a return to Milan, saying: "Zlatan is an interesting character. He keeps me very busy & you need this kind of players like what happened with Beckham few years ago.
"He is 38 years old & has now been signed by Milan, one of the biggest clubs in the world."
Ibrahimovic previously had two successful seasons with the Rossoneri, who are currently 11th in Serie A and on their second manager of the season, scoring 42 goals in two years before moving to Paris Saint-Germain.body check tags ::
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