But Hargreaves thinks Manchester City hiring Pep Guardiola is the only reason Mourinho is now in charge at Old Trafford.
He told the Manchester Evening News: "Mourinho is at Manchester United because Pep is at City.
"United were not completely thrilled about signing him even a few months ago. But Guardiola’s arrival at City spooked them."
The Red Devils decided to axe Van Gaal despite him winning the FA Cup in his final match.
But Hargreaves feels had City not secured a mega deal for Guardiola, United could have been tempted to stick with the Dutchman for the final year of his contract.
Mourinho has kicked off his spell as manager by signing defender Eric Bailly from Villarreal in a deal worth £30m.
He has also secured new contracts for Michael Carrick, Marcus Rashford and Cameron Borthwick-Jackson.
Mourinho will face Guardiola for the first time in the Premier League when the two sides meet at Old Trafford on September 10.
