The club's board is said to be guarding their coffers closely and want to get a tighter grip on spending before agreeing to fork out any more money on new players.
Having released their financial results back in September, the club revealed that their wage bill had gone up by by 13.5% which translates to a total of £263.5m spent on paying their stars.
Mourinho has spent £285m on six major transfers in his two-year tenure in charge of the Red Devils. And the club have only made £38m from notable sales, despite 16 players being shown the exit since the Portuguese's arrival.
Only Memphis Depay (£16m) and Morgan Schneiderlin (£22) left the club holding significant sums upon their departure, although United have also been relieved of high earners Wayne Rooney and Bastian Schweinsteiger.
Former Southampton full-back Luke Shaw set United back £27m when he joined three years ago, but he has failed to make a single start this season. It is believed that Shaw will be one of the first to depart if the Old Trafford side do decide to cut players in January.
The 22-year-old has already been linked with a move to Turkish side Fenerbahce, with reports claiming that negotiations with United already underway, although Shaw's former club Southampton are also reportedly an option.
Marouanne Fellaini, who seems to be a Mourinho favourite, could leave next year as well, as he will be free to talk to other clubs in January, based on his current deal expiring at the end of the season.