The 31-year-old former England captain won five Premier League titles, the Champions League, the Europa League, the FA Cup and three League Cups, scoring a club record 253 goals.
"I think he’ll get the welcome that he deserves," Mourinho told a news conference ahead of Everton's league visit on Sunday.
"Sometimes the word legend comes too easily (but) he's a real legend of the club. The number of appearances, goals, trophies – clearly he's one of the most important players in the history of Manchester United.
"I think the stadium will show him the respect he deserves. I hope before the match and after but not during it.”
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With Paul Pogba facing a spell on the sidelines with a hamstring injury, Mourinho believes midfielders Ander Herrera, Marouane Fellaini and Michael Carrick can step up to the challenge of replacing him.
"We have players waiting for an opportunity," Mourinho added. "He started the season really well, we’ve had one match per week we've been going with the same players.
"Honestly, we miss Pogba and we need him but we have good players. Ander Herrera, Marouane Fellaini, Michael Carrick - they're waiting for a chance and they are ready."
Mourinho said left back Luke Shaw is back in contention for a place in the squad after recovering from a long-term foot injury, but defender Marcos Rojo still faces some time out of action due to a knee problem.
United made a flying start to the campaign with three straight victories before being held to a 2-2 draw at Stoke City last weekend.
(Reporting by Hardik Vyas in Bengaluru, editing by Ed Osmond)
