The Red Devils manager has previously suggested that calling upon an established member of the senior squad for the 2017 European Championship in Poland “makes no sense”.
He has, however, now conceded that the decision lies outside of his control, with Gareth Southgate expressing a desire to see the 19-year-old included in Aidy Boothroyd’s ranks.
The Football Association will now have the final say, with United prepared to begrudgingly accept that they have little influence in proceedings.
"I don't think my opinion becomes important," Mourinho said.
"The power is in the Football Association's hands and they are going to make the decision which they think is the best decision.
"Whether I agree or disagree, my opinion is not important.
"I don't want to discuss because maybe it will end with you using my words and my words are not strong.
"I know I am the manager of Man United, I know that, but I have no right, no legal right in this situation.
"They [the FA] are going to do what they want to do with Marcus."
Rashford has made 40 appearances for United this season, with only Zlatan Ibrahimovic and Paul Pogba featuring in more fixtures under Mourinho.
He also formed part of England’s squad at Euro 2016 last summer, with an exciting young talent seeing little break time.
Mourinho, though, believes that the experiences will stand him in good stead and has refused to call on the FA for a rest period to be granted to his forward.
"What is clear is, by playing in the Premier League, in Europe, in the cups, he is having an amazing experience," the Portuguese added.
"After the hurricane that he was last season, when he came in, this year is giving him a hell of an experience.
"And because he is such a good boy, such a good professional, I believe this is a fantastic learning experience for him.
"We believe in Marcus, that's not in doubt."