Mourinho is expected to replace sacked Louis van Gaal, with talks ongoing between his agent Jorge Mendes and United officials.
But it has emerged that Chelsea still own the 'Jose Mourinho' name as a trademark - meaning United may need to pay a six-figure sum for the rights.
However, the issue will not scupper any deal, which is expected this week.
Discussions will now enter a third day, despite the deal to bring the 53-year-old former Chelsea boss to Old Trafford being largely complete. On Wednesday, Mourinho told waiting reporters at his home in London that he was going to Portugal.
What is the hold-up?
Chelsea registered both the name Jose Mourinho and his signature as a European trademark in 2005, meaning 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.
Chelsea registered both the name Jose Mourinho and his signature as a European trademark in 2005, meaning 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.
