Manchester United boss Mourinho wanted Mandzukic to provide competition for Romelu Lukaku up front.
Unconvinced by the form Anthony Martial and Marcus Rashford displayed in Lukaku’s absence last season, the Red Devils manager made a striker one of his top priorities.
Ultimately, Manchester United missed out with Mandzukic choosing to remain at Juventus.
And Italian website Calcio Mercato claim the Croatia international opted to stay in Turin because of Juventus boss Massimiliano Allegri.
United endured one of their worst transfer windows in recent memory.
At the start of the summer, Mourinho was targeting five new faces as he plotted a way to dethrone Manchester City as champions of England.
However, he ended the transfer window with Fred, Diogo Dalot and Lee Grant his only new recruits.
Calcio Mercato claim Mourinho was personally involved with trying to bring Manduzkic to Old Trafford.
And United were supposedly willing to offer the Croatia hitman a salary of up to £4.5million a year.
Yet Manduzkic chose to stay put because of Allegri.
The striker has been at Juventus ever since signing from Atletico Madrid back in the summer of 2015.
Allegri has shown faith in him since, despite having the likes of Gonzalo Higuain, Paulo Dybala and now Cristiano Ronaldo at his disposal over the years.