The unusual sticking point has prevented the widely trailed formal announcement that Mourinho will succeed Louis Van Gaal in the Old Trafford hotseat. Mourinho is understood to have agreed a three-year contract, reportedly worth 36 million pounds.
But British media are also reporting that Chelsea are demanding United pay a sum running into millions of pounds to sign over three separate trademarks of Mourinho's name, one of which the club have owned since 2006, during his first spell in charge.
Although the trademarks are limited in scope - reports say they cover secondary items like computer games and teddy bears - the area is important enough to United, who have a diverse portfolio of global sponsorhips, to require resolution.
The delay has surprised sports rights experts. They have questioned why Mourinho apparently signed over his own image rights, which are a huge driver of revenue.
“It is pretty uncommon for a manager of his stature not to have full control over the rights to his name and image, and pretty rare for a club to retain rights independently of a manager,” Julian Moore, a sports rights lawyer at Pinsent Masons, told Reuters in a telephone interview.
Chelsea believe they are entitled to compensation for allowing United to market their new manager on specific items.
A similar conflict arose when Mourinho first left Chelsea in 2007 to join Inter Milan and then Real Madrid, but the London club allowed their former manager's name to be used by those clubs under licence.
The Times reported that Chelsea had two further trademarks on Mourinho granted by the European Union's intellectual property office in 2013. Although owning his name is now of little value to them, the club are believed to feel a direct commercial rival like United should pay for the privilege of using it.
The subject has formed part of extended negotiations between United Chief Executive Ed Woodward and Jorge Mendes, Mourinho's agent. Also requiring resolution are potential conflicts of interests between United's extensive list of commercial sponsors and Mourinho's personal endorsement deals, with cars, casinos and watchmakers reportedly requiring clarification.
“United will want to ensure they have cleared all rights because they have a complex web of interests around the world. They will want all rights sorted before hiring someone of this type,” Moore said.
United and Chelsea did not respond to requests for a comment on Wednesday.
Original source: United, Chelsea haggle over Mourinho trademark