Mourinho has regularly divided United's season into playing well with Pogba and struggling without the £89 million Frenchman.
"We have lost a very important player, one with an impact in the way we play and that is obvious," said Mourinho about his talismanic midfielder.
"This season, there was a Manchester United with Paul and there was a Manchester United without Paul. He impacts our style. For the next three matches we have to cope without Paul and try to win without him.
"It's not pessimistic. It's just a different way to play football. Do you think I have in my team a midfield player who can make the third goal at Arsenal? We don't. They have other qualities. Fellaini can score an amazing header. Matic can shoot from outside the box. Herrera can do other good things, but a midfield player to do and create what Pogba did in the third goal against Arsenal, we don't have."