And he will miss out on playing his former club on Wednesday night due to a hamstring injury, which will keep him out until the end of the year.
A report in the Independent claims Mourinho does not consider Sanchez to be a “certain starter” and is now not against letting him leave.
Sanchez is said to be unhappy at Old Trafford but any club that signs him will have to take on his wages which are believed to be in excess of £500,000-a-week.
Speaking on Friday, Mourinho said he was optimistic United would see the best of Sanchez again.
Alexis Sanchez has struggled for Man Utd (Image: Reuters)
Mourinho said: "When we speak about Alexis, I think you should ask why every time a player is not playing in Manchester United, there is always a rumour.
“There is always a problem. It's only here.
"In Chelsea when Willian doesn't play there is no problem with Willian and (Maurizio) Sarri.
“In Man City, when Gabriel Jesus is not playing for weeks, there is never a problem. It is just a normal decision.
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Jose Mourinho has been unable to get the best from Alexis Sanchez (Image: Reuters)
"Here is the only club where every day the manager has problems with the players.
“You make me feel very, very special because I am the one who is different from everybody else.
"But speaking about Alexis - a frustrating season. It's a season where he is not playing a lot, where he had small injuries, where he now has a big injury.
"I don't like and don't believe in the word curse but I have to admit it was probably a very unlucky six months, and we expect the new year brings better things for him."