The 23-year-old, who became the world's most expensive footballer when he sealed an £89miillion return to Old Trafford, missed the start of a season with suspension and has only been training with his new club for 11 days after an extended break at the end of his Euro 2016 excursion.
However, Mourinho is confident he is in a condition to face the Saints, even if he is unlikely to last the 90 minutes.
"We played with some players against Leicester with less training than Paul," the Portuguese said.
"We had guys coming back from the Euros, who were on holidays, had one week of training and they played against Leicester (in the Community Shield), not at the top of their game, not ready for 90 minutes but they played and performed and it was a good way for them to accelerate that process
In this moment t hey are in the building-up process of their form
"Paul has been training for more than a week, around 10, 11 days, adaptation is really easy because he is a boy from here, he knows the club, he knows everybody
There's no need for time to adapt
"He needs time to build his condition and his understanding in the way the team tries to play
Yes, he's ready to play
Ninety minutes? I don't believe
Super performance? I don't believe
But in condition to accelerate his process of integration in the team, that's for sure."
Given the hype which has surrounded Pogba's return to Manchester, he will be assured of a huge reception on his homecoming at a venue which opposing teams have viewed with less trepidation in recent years.
Friday's opponents Southampton have emerged from Old Trafford with three points in each of their most two recent campaigns, while Norwich, West Brom and Swansea have also recorded victories in the previous two terms.
When Mourinho, who assumed the reins in the summer, was asked if he can help restore the "fear factor" to his home stadium, the boss placed the onus on United's fans to be more vocal.
"Not me," he said
"The team, yes
And the fans too
I think everything starts there - the relationship between the team and the fans
"If at Old Trafford, a couple of thousand away opponents can be more noisy than 70-something thousand then we are in trouble
It means that there is no connection between the team and the supporters.
"If there is connection, I think that factor of being really strong at home has to be back
Everything starts on that relationship between the team and the fans.
"If the fans feel that connection, they want also to play, and if the fans play then there's no chance for the opponent."
Source : PA
Source: PA