The £27 million signing began the season superbly but has only started one of United’s last 11 league games.
Boss Mourinho has omitted Mkhitaryan from his matchday squad eight times in the last 10 weeks but expects him to feature against Stoke next.
But, asked if the Armenian will stay at Old Trafford, he replied: “Every player has a price. It doesn’t matter who. It doesn’t matter the level. It doesn’t matter the prestige, or the status. I am not the kind of blind manager – blind in the sense that, this player is untouchable, he can never be sold.
“So when the transfer window is open, it’s also open for any club that is interested in our players. Then it’s up to us to make the decision: yes or no. It’s up to us to make the right price.”
Mourinho has admitted that Manchester United cannot buy their way to the title because Manchester City’s lead is too big.
But the United boss is willing to change his original plans not to sign in January if the right player becomes available and he could swoop for City target Alexis Sanchez in a £35 million deal.
United have emerged as the favourites to bring in Arsenal’s unsettled Chilean, who is a long-time target of Pep Guardiola and out of contract in the summer.
And Mourinho reckons that if United get the right deal now, it will mean he makes one fewer signing in the summer.
“If there is on the table a fantastic opportunity, you fight for that fantastic opportunity,” he said. “If in the winter market you do something, you have to do something that stop you to it again in the summer.”
Mourinho added: “I think it’s a very comfortable advantage and. I don’t think it’s about the transfer window for us, or the other teams close to us.”