Pogba has not had any pre-season warm-up matches because of his late start back following France’s appearance in the Euro 2016 final.
But Mourinho says that after 10 days training following his world record £89m transfer from Juventus the 23-year-old midfielder is fit enough to face Southampton and the fact he already knows many of his team-mates and staff - not to mention the stadium - from his previous spell at the club make sit easier to give him his debut.
He added, however, that he will not complete the 90 minutes and will have to use competitive matches to get himself up to full speed.
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Jose Mourinho confirms Paul Pogba will start for Man United against Southampton
“Some players with less training than Paul played against Leicester in the Community Shield,” he said.
“Some of them came back from the Euros, trained for only a week and played in that game.
“They were not ready for 90 minutes at that moment but Paul has trained for more than a week, he’s had 10 or 11 days and he is adaptation [to the club] has been really easy.
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“He knows everybody here so he doesn’t need any time to adapt.
“Yes, he is ready to play but not for 90 minutes or [produce] a super performance. “
Pogba’s made seven substitute appearances for the senior team in his first spell with United between 2010-2012 but never started a game so tomorrow will be his full debut.