Mourinho is the favourite to replace United manager Louis van Gaal, but may have to accept a pay cut to take over at Old Trafford.
Chelsea gave Mourinho a new contract worth around £10 million a year in August, but the Portuguese could expect about £6 million a season to succeed van Gaal. Under the terms of his Stamford Bridge departure, it is believed Mourinho will continue to be paid by Chelsea until he finds another job.
It is also understood, however, that Chelsea will have to make up the shortfall in any wage cut Mourinho accepts at a new club until the end of this season.
That could mean that Chelsea have to pay Mourinho around £1.5 million to manage United if he replaces van Gaal early in the new year. Both Mourinho's camp and Chelsea refused to comment on the terms of the 52-year-old's departure. But the prospect of Chelsea paying him while in charge of United will anger Stamford Bridge fans, who did not want Mourinho to be sacked and showed their support for him during last week's victory over Sunderland.
The possibility of Mourinho replacing Rafa Benitez at Real Madrid before the end of the season and Chelsea topping up the wages of the Portuguese at the Bernabau would be more palatable.
Reports in Spain claim Benitez could be sacked before Real's next game at home to Real Sociedad on Jan 30 and that president Florentino Perez has already made inquiries about taking Mourinho back to the club. Chelsea interim manager Guus Hiddink expressed his sympathy for both Mourinho, who he has replaced, and fellow Dutchman van Gaal.
"The titles he won, many titles," Hiddink said. "Lots of respect for that. But, nevertheless, things happen in football and people take the decision they've taken."
On van Gaal, he added: "They [United] are struggling as well, that's for sure. That also has much to do with the improving Premier League."