United were heavily linked with a move for Dier during the summer transfer window and reportedly saw three separate bids for the versatile England international rejected. In July, the Observer claimed that while the player was open to joining United after being displaced as Tottenham's first-choice defensive midfielder by Victor Wanyama last season, the Manchester club saw bids of £25m, £30m and another close to £40m all rejected by Spurs chairman Daniel Levy.
Shortly afterwards, United shifted their attention to Matic, signing the Serbia international for a reported £35m. The towering midfielder instantly became a hit at Old Trafford and has been an ever-present figure in Mourinho's Premier League midfield so far this season.
This Saturday, Matic and Dier could come up against each other as Spurs travel to Old Trafford, looking to leapfrog United and move into second place behind leaders Manchester City.
Speaking at a press conference ahead of that contest, the United boss suggested Matic had always been his preferred option – but did not think the former Chelsea star was a realistic option at the time.
"I have the player that I want to have," Mourinho said. "Probably I have the player I didn't think it was possible to have but we got the player I really wanted."
Mourinho was also pushed on Luke Shaw's future at the club. The 22-year-old left-back has made just two appearances this season, both off the bench in the Carabao Cup with recent reports suggesting there are fears his relationship with the manager has completely broken down.
An extract to emerge from Mauricio Pochettino's book Brave New World: Inside Pochettino's Spurs on Thursday quotes Shaw lavishing praise on his former Southampton manager, suggesting the Argentine would like to have him back in his squad one day.
Mourinho however was not upset by those comments, even complementing the defender for his honestly before insisting the England international can still fight his way back into contention at the club.
"He has a future here, I think he has, but the situation is not easy," said Mourinho. "He comes from injury after injury after injury, he needs two, three, four, five, six matches in a row to play, to make mistakes, to get condition, to get match fitness and I cannot give him that in this moment.
"If he was a central midfield player yes, because we have only two but at left-back we have so many options that the situation is not easy. He's in the squad, he works maybe the opportunity comes."