Michael Carrick, who has been at Manchester United since 2006, is expected to hang up his boots at the end of the season and move into a coaching role at the club.
This leaves a vacancy in the midfield, and Mourinho has confirmed that one of his priorities this summer will be to find someone to fill the England international's boots.
"We need to sign a midfield player," Mourinho said, speaking in the lead up to his side's FA Cup tie with Huddersfield, which they won 0-2. "Because we are going to lose Michael Carrick. Of course, we need balance in the team."
"Some of you [the media] keep saying that we are going to buy that striker, that winger, that left winger, that right winger. You can accuse me of many things, but you cannot say that I lied to you. When I don't want to say things, I don't say [them]. But I don't take you in other directions. We are looking and we are going to try to sign a midfield player."
According to 'The Independent', Mourinho's search has taken him to his old club Real Madrid, where he has his eyes on German midfielder Toni Kroos.
Kroos, who joined the club in 2014 is not out of favour at Real, but with Zinedine Zidane's side looking to make some big signings in summer they may need to free up funds by letting go of some big names.
If they cannot land Kroos, they may also turn to Borussia Dortmund's Julian Weigl, another reported target for the 'Red Devils'.