Image rights negotiations are delaying Jose Mourinho's appointment as Manchester United manager.
It has emerged that Chelsea still own his name as a trademark and could demand a six-figure sum from United before any deal is concluded.
However, the issue will not scupper his appointment at Old Trafford.
Mourinho is expected to be named as Louis van Gaal's replacement after the Dutchman, 64, was sacked on Monday despite winning the FA Cup.
The deal to bring Mourinho to Old Trafford are largely complete, but discussions between his agent, Jorge Mendes, and United officials will now enter a third day.
On Wednesday, former Chelsea and Real Madrid boss Mourinho, 53, told waiting reporters at his home in London that he was going to Portugal.
What is the hold-up?
Chelsea registered 'Jose Mourinho' and his signature as a European trademark in 2005, which means they can use it to sell merchandise such as toiletries, technology, clothing and jewellery.
Sports lawyer Carol Couse told BBC Sport it was "really unusual" for an individual not to own the trademark to their own name.
"If United had a brand of Mourinho clothing, it would be in breach of the trademark Chelsea currently own," said Couse, of law firm Mills & Reeve.
What are the possible solutions?
Mourinho cannot override the trademark, so the options are:
- United do not use Mourinho's name against the exhaustive list of items that Chelsea have registered - from umbrellas to watch straps, lingerie and talcum powders.
- United pay Chelsea for a licence so they can use Mourinho's name on club merchandise
- United ask Mourinho to buy the trademark back
- United challenge the trademark if they think they can prove it has not been used by Chelsea
Couse pointed out that Mourinho has managed Inter Milan and Real Madrid since the trademark was registered, suggesting the Italian and Spanish clubs both found a way around the sticky issue.
"They have either acquired the rights from Chelsea or managed the use of his name," she said.
As for a licence, Couse estimated that it could cost United "hundreds of thousands of pounds" but said it might be worth the investment.
"If Chelsea didn't grant a licence, every time United used Jose Mourinho's name in a commercial capacity against those products, Chelsea could sue Manchester United," she said. "I would suspect United would rather just pay a licence fee."
Any other issues?
There is also potential conflict between Mourinho's personal deals and United's own sponsors.
For example, he has a contract with car manufacturer Jaguar, while United's shirts sponsors are Chevrolet.
"I don't think that in itself would hold up any negotiation," said Couse.
"A lot of world-class players go to Manchester United with their own personal deals. Mourinho's deals will be in a personal capacity."
Couse said United cannot force Mourinho to drive a Chevrolet car or wear Chevrolet clothes outside of club capacity, but they could pay him an incentive to buy out the Jaguar deal early.
Chelsea declined to comment when contacted by BBC Sport.
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