Mourinho says United is only among the contenders.
The Spanish club has reportedly come to an agreement with Monaco for the 18-year-old.
The Manchester United manager is renowned for his feuds.
The Premier League continued its heavy spending last week.
The club has already spent more than £100 million this summer.
Premier League clubs' spending is far from over.
United won't be held to ransom over transfers.
The Premier League champion confirmed the signing on Wednesday.
The Italian manager missed out on the signing of Romelu Lukaku, who went to Manchester United instead.
The London club has made some big moves in the transfer market.
The Premier League is set for record spending this summer.
The Premier League's giants are spending big this summer, very big.
The £75 million man scored in a 2-1 win over Real Salt Lake.
The winger looks to be on his way from Inter Milan.
Controversial striker Costa moved from Atletico Madrid to Chelsea in 2014.
The Premier League's biggest teams are preparing for more deals.
Spending in the Premier League reached £600 million for the summer.
The Englishman returned to Everton earlier in July from Manchester United with forward Romelu Lukaku moving in the opposite direction in a big-money deal.
De Gea almost moved to Real two summers ago.
Winger Ivan Perisic looks unlikely to go to United this summer.