The deal can go ahead after Manchester United announced they had signed Juan Mata for a club record fee worth £37.1m.
The 25-year-old completed his medical over the weekend and put pen to paper on a contract thought to be worth around the £150,000-a-week mark.
Mata's move to Old Trafford brings an end to his two-year stay with Chelsea, where he was twice voted the club's player of the season and was part of the side that claimed Champions League glory in 2012.
"I am thrilled to be joining United. I have enjoyed some very happy years at Chelsea but the time has come for a new challenge. United is the perfect place for me and I am excited at the chance I have to be part of the next phase in the club's history," Mata told the club's offical website.
"Chelsea is a top club and I have many friends there but you cannot turn down the chance to join Manchester United. I look forward to helping the manager and the team be successful in the coming years."
Meanwhile Mourinho has revealed Chelsea will speak to 21-year-old Egyptian winger Salah after he caused controversy in the summer when he did not shake the hands of players from Jewish club Maccabi Tel Aviv in a Champions League qualifier, changing his boots on the sidelines instead.
The Stamford Bridge club have a Jewish owner in Roman Abramovich, and Mourinho said the matter would be dealt with.
“We know which owner we have and the variety of players we have, so this is a fantastic club to support a young boy at 21 to grow up and be strong.”
It follows the news that Chelsea midfielder Michael Essien, 31, was at AC Milan for a medical ahead of his free transfer.
Chelsea to complete £12m signing of Liverpool target Mohamed Salah
Daily Star | Jan 26