They say United will hold talks with Juventus over the forward within the next three weeks.
It’s also claimed Mandzukic could even head to United in December to train with his new side before the transfer window opens.
United executive vice-chairman Ed Woodward has been vocal on the club’s transfer plans, insisting the Red Devils have a clear plan going forward.
The Red Devils spent around £150m in the summer, landing Harry Maguire, Aaron Wan-Bissaka and Daniel James.
Man Utd transfer news: Mario Mandzukic could join (Image: GETTY)
Ole Gunnar Solskjaer has also given game time to the club’s youngsters, with Mason Greenwood, Angel Gomes, Tahith Chong, James Garner and Brandon Williams all appearing this season.
And Woodward insists United have a clear plan moving forward ahead of the January transfer window.
"We have a clear vision in terms of football philosophy and recruitment," Woodward said.
"The significant investments that we have made in recent years in areas such as transfers, recruitment infrastructure, analytics and our Academy are already beginning to bear fruit.
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Man Utd transfer news: United are keen to spend (Image: GETTY)
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Man Utd: Mario Mandzukic may not sign with club says expert
"We are very proud to be shortly approaching a milestone 4,000th game featuring an Academy player, and we are particularly optimistic regarding the considerable young talent currently coming through.
"Our ultimate goal is to win trophies by playing exciting football with a team that fuses graduates from our Academy with world-class acquisitions.”
United are back in action in the Premier League this weekend against Sheffield United.