The World Cup-winning Germany star has been completely frozen out at Old Trafford since Mourinho’s arrival as manager.
He has yet to feature in any of United’s squads this season and has been banished to train with the Under-21s.
In a statement released earlier this week, Schweinsteiger said he remained committed to the club and will be ‘ready if the team needs me’.
But Mourinho says the 32-year-old is out of his plans and will not play if he decides to stay.
“I think it’s very difficult to happen,” he said, when asked on Friday if there was any chance Schweinsteiger could play for United at all this term.
“I’m not saying it’s impossible. I’m saying it’s very difficult.
“We have a decision completely made about (Paul) Pogba, (Ander) Herrera, (Morgan) Schneiderlin, (Marouane) Fellaini and Michael Carrick (Schweinsteiger’s fellow central midfielders).
“We have five players for two positions. It’s very difficult that an opportunity will arrive.”
Mourinho has been criticised for his treatment of the 120-cap Germany legend.
Karl-Heinz Rummenigge, the president of Schweinsteiger’s former club Bayern Munich, has accused United of showing “a lack of respect for such a worthy player”.
And Mourinho couldn’t resist a dig at the Bayern chief on Friday, saying: “I thought after I read some quotes from people at Bayern Munich that they would run to Manchester to bring him (Schweinsteiger) back, but no, that did not happen.
“I am quite surprised that Mr Rummennigge is not here now to take him back.”
Schweinsteiger has two years left on his United contract, and in terms of the prospect of him staying on at United despite not playing, Mourinho said: “I cannot answer for him. It’s his life. It’s his career.
“He has a contract with Man United and has the right to make that decision to stay.
“That’s not a problem for us. Football is made of decisions. I did that all my career. Not just me, everyone does. Some players react in a different way and have other kind of decisions.
“Bastian is not speaking a lot. He gave this last statement, which he is completely free to do in an objective and polite way like he did. There are no problems at all.”