United decided against offering Ibrahimovic a contract extension with the former Sweden worldwide initially expected to be sidelined until the New Year.
'We opened our door for him to recover with us and then to make a decision.
The striker is also being linked with a move to LA Galaxy, United's first opponents on their tour of the U.S. at the StubHub Center in the early hours of Sunday morning, after promising a major announcement.
Lukaku, 24, becomes the eighth United player to be given the number nine since the introduction of squad numbering in 1993, with Brian McClair, Andy Cole, Louis Saha, Dimitar Berbatov, Radamel Falcao, Anthony Martial and Ibrahimovic all wearing it before him.More news: Wimbledon 2017: Sachin Tendulkar cheers for Roger Federer at Centre Court
"It's possible, it's open, of course". "Old Trafford, Carrington is open for him to recover and be one of us and, at the same time, let's make a decision that will make us all happy".
'There was a space and time for everyone to think, to feel, to decide and, from his point of view, he made the decision to still want to play football at the highest level. He didn't want to hide behind such an awesome injury.
"He did not want that, he was not happy with his finish (to the season) and not playing".
He was widely expected to sign a new short-term contract but a cruciate knee ligament injury will keep him out until the end of 2017, although he has been doing his rehab at the club's AON Training Complex. "And if that decision is for him to stay and for us to wait let's say until December - I don't think before December he can be back to competitive football - why not wait for such a good player who gave us so much?"