According to The Daily Mail, the Portuguese is reportedly becoming increasingly detached from the club and is beginning to spend less time in Manchester.
The former Chelsea boss resides in London and travels up north by train, opting to stay in hotels rather than look for more permanent accommodation.
Mourinho is also growing frustrated at falling so far behind fierce rivals Manchester City at the top of the Premier League.
The 54-year-old has publicly criticised the United board for not backing him in the transfer market, despite spending £300m since taking over last summer.
A Mail source said: “Jose seems to be having third-season syndrome a year early with us.”
Despite regularly travelling by train, Mourinho is reported to have used a private jet over Christmas, which wasn’t paid for by the club.
The Mail claim that Mourinho is quickly becoming a recluse at the club and eyebrows have been raised at the way he attacked United legend Paul Scholes.
The former midfielder criticised Paul Pogba for recent performances and Mourinho chose to respond to Scholes, ignoring criticism from several other pundits.
The ex-Real Madrid boss has previously been linked with a switch to PSG, with current manager Unai Emery facing a battle to keep his job.
“Paris Saint-Germain would be low-hanging fruit for him,” commented another Mail source.
United are back up to second in the Premier League after leapfrogging Chelsea with a 2-0 win at Everton on Monday.
They remain 15 points behind City, with many conceding the title race is already over.
Mourinho’s side return to action on Friday as they host Championship side Derby in the FA Cup (8pm).