José Mourinho says Real Madrid would never go behind his back to sign David de Gea because he and Florentino Pérez, the Spanish club’s president, are “big friends”.

Pérez said “someone is messing around there with De Gea”, when asked this week about stories linking the Manchester United player with Madrid, though he did not rule out moving for the goalkeeper in the summer.

De Gea, a much valued member of Mourinho’s squad, has since said he is happy at United but added “the future is the future”. He came close to joining Madrid on the final day of the 2015 summer window.

Mourinho, who managed Real for three years until 2013, was asked about Pérez’s comments. “With Mr Pérez and his right arm José Ángel Sánchez [director general], they are some of the people in football that I can say I did not work for them and then it is over,” he said. “I can say that we are friends forever, big friends. I like them a lot. Friends speak, friends are open, friends are honest.

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“So if at the end of the season I want one of their players or they want one of our players we will not do it through the press. We are going to exchange messages. We will be very direct. So they are one of the clubs that I am not worried about at all.”

Of the prospect of De Gea definitely being at United next season Mourinho said: “I have nothing to say because I am not going to speak about hypothetical things. The only thing that is real is that he is my player, I am happy with him, I know that he is happy with me and there is nothing else, absolutely nothing else.”

United, who are unbeaten in 15 league games, entertain Watford on Saturday. Their last match was Sunday’s 3-0 win at Leicester City in which Henrikh Mkhitaryan scored and operated at No10 after the manager had previously fielded him in wide positions.

Mourinho said: “I will use him everywhere I need. I played him left-back [once]. He is ready, his mentality has changed, his profile of a player does not change, but the mentality and approach changed. He is ready to play for us. What we did last weekend is something we will try and do more and more.

“Start with a system, try to surprise the opponent, then the team is ready to go back and to change during the match. You can only do that with maturity, with some work with time and knowledge with what your players can do. During the week we trained for both things. I don’t need to change players, just change the roles on the pitch. So, be ready, after five, 10 or 20 minutes we are going to change. We have more and more capacity to try to do these things to try and surprise opponents and create difficulties.”

Mourinho is pleased with Marcus Rashford’s development in the forward’s second campaign in the first team. “When he is on the pitch he tries, he always gives something,” he said. “I know that last season under no pressure, last season in front of the goal, the goal was bigger. I know this season the expectations are higher, the pressure is higher and the goal is smaller.

“He is still a kid but not the new kid in town any more. Next season will be very, very good for Marcus because this season he is getting experience at this level of responsibility of being a professional player at a club like Manchester United.

“He said something the other day that made me really happy – that he is learning so much in the technical meetings and training sessions so I think his future will be brilliant. His present is good and we need him.”

Mourinho suggested Zlatan Ibrahimovic may have only one more year left at the highest level and is confident it will be at United. The Swede is out of contract at the close of the season, though United hold an option to extend this for another 12 months. Although this has yet to be signed, Mourinho believes it is a formality.

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“I’m totally convinced he is going to stay,” he said. “He came with the intention to stay two years but in the minds of everyone the first year is going better than every expectation. He knows we are going to try again to improve next season and try to share with him in a fantastic way probably the last year of his career at the highest level.

“So I’m convinced that he’s staying, he’s adapted to the club, to the situation, I don’t see any problem with his family. I give him the possibility of an extra day off to go to Sweden, he doesn’t want this ever, so I’m totally convinced he is going to stay.”

Mourinho also stated United would have a “small” market in the summer window, the target being a maximum of four players. “Independent of the numbers, can you spend 1, 10 or 100 million, it’s also the philosophy – we prefer to bring two three or four players, players that feel an idea, a football we try to play, that can improve our squad,” he said. “We are not interested in signing six or seven or sell six or seven. We are not going to play this game,” he said.

“We are stable, so we think our market in the summer will be soft, will be natural – some players to leave, some players to come but in a very natural way so I think the word Ed used was a good one. You work with the players and you know the players better - even in relation to this everything is balanced, I’m not negatively surprised with anyone, I didn’t have an incredible impact with some player. So everything is balanced and I think our summer will be quite small.”