The Belgium international moved to the Red Devils in a £75m deal from Everton in the summer transfer window despite interest from his former club Chelsea.
Ibrahimovic was released at the end of the 2016-17 season following the expiration of his contract as the centre-forward continued his rehabilitation from a serious knee problem.
The veteran striker was expected to re-sign with the Red Devils and Manchester United offer the 35-year-old a new one-year deal in the final week of the transfer window.
Ibrahimovic scored 28 times in his first season after the Manchester United number nine moved to Old Trafford from Paris Saint-Germain in a free transfer last summer.
However, Lukaku inherited the No9 shirt from Ibrahimovic following his big-money move to Manchester United, before the Red Devils gave the Swede their number 10 shirt last month.
And the Belgium international has revealed the conversation that he shared with Ibrahimovic before taking on the challenge of emulating some famous Manchester United number nines.
“I didn’t want the number 10, I wanted the number nine, so I called Zlatan and asked him,” Lukaku told BT Sport.
“He said that I could take the number nine and he would take the No10. I said I was looking forward to him coming back.”
Manchester United are sitting at the top of the Premier League table thanks in part to Lukaku’s four goals in four games.
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