The former England captain is tipped to earn £250,000 per week and join Ronald Koeman's Merseyside revolution.
The 31 year-old had been linked with moves to the MLS or the Chinese Super League.
He is with Sky Bet to head back to Everton on the back of rumours he is close to agreeing a Goodison Park deal this week.
With Mourinho likely to add the likes of Real Madrid striker Alvaro Morata to his attacking ranks in the summer transfer window, Rooney could feature even less often for United in 2017/18.
SunSport exclusively revealed last night that the England worldwide will become a Toffees player by the end of the week.
Manchester United are due to jet off to the United States for their pre-season tour on Sunday.
It is believed United will allow Rooney to go on a free provided he does not ask that the final two years of his contract are paid up.
Rooney - United's record goalscorer with 253 efforts - always preferred a move to Everton and said he wouldn't play for other Premier League sides.
The club could also make a move for Arsenal's Olivier Giroud once the Gunners have completed a deal for Alexandre Lacazette. Loved by millions, derided by just as many, the Liverpool-born striker come midfielder has been one of the iconic figures within the Premier League over the last 12 years.
That would have been nearly impossible, had he made the move to China, and it is also understood Rooney's representatives were put off by the standard of football there.