"Twenty-five per cent means one of four," Mourinho told a news conference on Friday. "We got a central defender who can play many other positions which is very important. Victor can play right-back and centre midfield.
"We have a central midfielder and striker, so obviously another player would be one coming from the sides."
Mourinho acknowledged this week that Real Madrid's Gareth Bale was out of reach after the Welshman started for the Spanish side in their 2-1 European Super Cup win over United.
The manager confirmed that the Manchester club is in talks to re-sign striker Zlatan Ibrahimovic, who is recovering from a knee ligament injury.
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The 35-year-old, who scored 28 goals for United last season, has been at the club during his rehabilitation and Mourinho said the Swede could feature in the second half of the season.
"You know he's injured, he needs time to recover, he's not ready to play tomorrow," Mourinho said.
"It's not something urgent, that we are desperate to have it done or not done, I just think that he was very clear by showing what he did last year was not enough for him.
"He wants more at the highest level so we are having conversations and we are discussing the possibility of him to stay with us for the second part of the season."
Centre-backs Eric Bailly and Phil Jones return to the Manchester United squad for West Ham's visit to Old Trafford on Sunday, after being suspended for Tuesday's Super Cup defeat by Real. Defenders Luke Shaw, Marcos Rojo and winger Ashley Young are out with long-term injuries.
(Reporting by Hardik Vyas in Bengaluru; Editing by Susan Fenton)
