The 26-year-old has not featured since September due to an ankle injury and returned to the north-west at the end of last week after a spell of rehabilitation in Miami.
But Pogba will not be fit for Wednesday's reunion with former United boss Mourinho, who the World Cup winner regularly clashed with towards the end.
Manager Ole Gunnar Solskjaer said: "No. Paul's not ready, no.
"He's still a bit away but he's working hard so let's see. He's out on the grass, so let's see how long it will take."
United looked light in midfield at the start of the season and that issue has been compounded by injuries.
In addition to Pogba, influential midfielder McTominay has missed United's last three matches with an ankle issue and Matic has not been seen for two months.
"They're touch and go," Solskjaer said. "So let's get this training session out of the way. We've got more games than this one, so of course I can't look at just the one game, we have got to look at long-term."
McTominay and Matic were trusty lieutenants under Mourinho, who Solskjaer expects to get a good reception when he returns to the Old Trafford touchline for the first time since his sacking last December.
"Very good reception," Solskjaer said of his predecessor. "Of course that's just a testament to this club and the supporters of this club.
"Of course they remember the two-and-a-half years he was here, he won trophies. I'm 100 per cent sure our fans will welcome him, and the staff and the club, everyone."
Mourinho was dismissed 12 months ago with United sixth in the Premier League standings, having won 26 points from 17 matches.