After spending the last two season in America with Major League Soccer outfit LA Galaxy, the Swedish striker returned to the San Siro on a short-term deal.
While he has famously worn the No.9 at his previous clubs, the 38-year-old took the No.21 jersey as Krzysztof Piatek, who was since loaned out, had the No.9 at time.
"If someone scored with the Milan Number 9 on his back, then I am happy," Inzaghi told Sky Sport Italia ahead of Sunday's Milan derby.
"So let's end this 'curse.' It's not right to retire the Number 9, because someone must always wear it, but I hope that Ibra – if he stays – decides to take it on, because he's got broad enough shoulders to carry it off."
Inzaghi added that he hopes to see his former side claim the spoils at the San Siro on Sunday evening.
"I was convinced Ibra would bring a lot to this team, even before his first goal, because he would never have accepted a return unless he was at 100 per cent. I know him and how much he cares about his profession, how he loves a challenge, but also winning.
"I hope it's a great derby on Sunday and I'll be happy if Milan win. Unfortunately, it's playing at the same time as Benevento, so it'll be strange not being able to watch it."