Mata is set undergo a medical on ahead of a proposed £37m transfer from Chelsea to the English champions having been given permission by the Blues boss.
An accord between the two clubs looks to have been reached shortly after Chelsea agreed a fee with Basel for Mohamed Salah who looks to have been lined up as a direct replacement for the 25-year-old.
Mata will become United’s club-record signing and a formal announcement is expected on Friday provided the playmaker comes through a medical on Thursday evening, Sky sources understand.
The Spain international did not train with Chelsea on Wednesday and is understood to have told team-mates that his departure from the club was imminent.
Chelsea are understood to be happy to sell and would make a significant profit on the man they signed for £23.5m from Valencia in 2011.
For Mata, the transfer would give him an opportunity for much more playing time with the World Cup in Brazil looming this summer.
All parties are keen for the transfer to go through, according to Sky Sports’ Spanish football expert Guilleme Balague
Meanwhile, Arsenal boss, Arsene Wenger, believes Mata’s impending sale to United is a sign that Financial Fair Play is working.
Chelsea have sanctioned the mid-season sale of Mata – the club’s player of the year in each of the past two years – despite the fact the deal will significantly strengthen a Premier League rival.
The Spain midfielder cannot face Chelsea this season – Mourinho’s side have played United twice already – but could yet affect the results of the club’s title rivals.
Wenger takes issue with the rules which allow such unevenness but believes the deal is less down to astute timing and more do to with balancing the books to stay in line with UEFA rules.
“I think it is a purely financial reason,” he said. “That is the first time I come to that conclusion with Chelsea.
“It means somewhere that Chelsea changes philosophy and they want to get on line with financial fair play. For me that is the main reason, and that is a good thing.
“We didn’t need the rules of financial fair play to be dictated to us because we imposed it on ourselves, like what should be the case for everybody.