It is expected to be a warm return to Old Trafford for the Dutchman, who was a key part of the 1999 treble-winning side before moving to Lazio in 2001 after three seasons in Manchester.
Stam's talents seems to have also passed into management, with the 44-year-old guiding Reading to third in the EFL Championship table in his first season at the Madejski Stadium. It is expected to be a tough test for the Royals, but Mourinho stated that he expects a warm welcome and a tough test from Stam's side.
"Everyone knows Jaap's history at this club," Mourinho told Sky Sports. "He's going to get a great reception from the fans."
"I think he prefers that I speak about him as a manager and not as a player," he stressed. "Because, as a player, everybody knows [Stam's ability]."
"As a manager, not everybody knows and I have to say what I feel," the coach admitted. "A team that plays like Reading, the manager has to be very good."
"So, I think the best compliment is to say that after analysing three or four matches of Reading," Mourinho added. "The way they play football, the way they are positive, the manager has to be very good."
Ready to play
The busy festive period continues for United with this their second game of three in eight days, with the crucial EFL Cup semi-final clash with Hull City coming up on Tuesday. Saturday's game could see a number of rotations, with one of them been the return of midfielder Bastian Schweinsteiger.
The German's only appearance came in the last five minutes of the 4-1 win over West Ham United, and the Portuguese coach hinted that the former Bayern Munich man could be appearing more throughout January with the hectic schedule.
"He’s selected again so he can start, he can be on the bench," he said. "But he’s an option for us."
"I think that’s the best way to describe [him]," the coach stated. "For many months he wasn’t an option; we made that decision."
"When we brought him back in the first couple of weeks," the Portuguese manager admitted. "He was not an option; he was obviously not ready to compete."
"Since then he’s been working very well and never an injury," he stressed. "His body is fine, he’s training very well and he’s ready."
"He’s an option he’s waiting for a chance to play," Mourinho concluded. "I think January is a good month for that, with so many matches."
Manchester United will take on Reading in the third round of the FA Cup at Old Trafford on Saturday, December 7 with kick-off at 12:30pm GMT.