The manager also hinted that the Spaniard could return for their match against Liverpool in the Premier League this weekend.
Read what else Van Gaal discussed below.
Good afternoon! Manchester United manager Louis van Gaal will be speaking to the media shortly as he prepares for the visit of Liverpool this weekend.
The Dutchman's side threw away a lead in their last outing, conceding twice in quick succession to slip to a 2-1 defeat at the Liberty Stadium. Following a goalless draw with Newcastle United the week before, United have seven points from their first four matches of the season.
Over the international break, David de Gea's future at the club has dominated the headlines. The goalkeeper was on the verge of joining Real Madrid on the Spanish league's transfer deadline day, but the paperwork was completed late. With just a year left on his contract at Old Trafford, there was a risk that he could leave for free at the end of the season, but the Spanish international has now penned a four-year contract extension.
With De Gea's immediate future more secure, the keeper could return to action this weekend. He hasn't been in the squad while the transfer speculation continued, with the manager concerned that he would be distracted.
Van Gaal has been speaking to the club's TV channel ahead of his press conference. He's confirmed that Andreas Pereira returned from international duty with an injury, but Michael Carrick is fit, while Phil Jones is still recovering from thrombosis.
The manager will be getting his press conference underway in a few minutes, so there's just time to remind you that there will be live updates from this match from 3.30pm tomorrow with Sports Mole, so make sure you join us again then to see if Manchester United can make it three straight wins over Liverpool.
Van Gaal has also hinted that David de Gea will return this weekend, telling MUTV: "You shall see, you never know. His head is empty now and that is important. He can focus, but we have to judge him in training."
The manager is ready to speak, so let's see what's on his mind this week.
Starting with David de Gea's new deal, Van Gaal tells reporters: "It is a confirmation of what I have always said, the transfers are a process. We didn't sell him. I believe a player has to want to play for a club. I'm very happy he has decided to stay. He was my best player last year. It's a happy end."
The team also completed a deal late in the transfer window for Anthony Martial, and the manager admits: "We could have waited until next year and his value be £10m more, but now we can build him up. I told Ed [Woodward] he is the best of his age, and we need a striker in the future, so if we wait a year he is more expensive."
Van Gaal reveals that Wayne Rooney and Michael Carrick approached him earlier in the season with concerns about the atmosphere in the dressing room: "[Carrick and Rooney] came to me and said the dressing room is flat. We want to say that to you because we want to help you."
James Wilson has been linked with a loan move away from Old Trafford, and Van Gaal admits: "It's the same with Januzaj. He should go to another environment to play more but he'll go to a Championship club."
Back to the arrival of Martial at the club, Van Gaal adds: "He must adapt. He's 19-year-old. You saw Di Maria struggle and he's 27, Falcao was 29. He needs time."
Van Gaal is asked more about the atmosphere in the dressing room, and he reveals: "I have a superb relationship with my players. Maybe you have to consider how many players are coming to the manager to say something. In my career as a manager I didn't have so many players who are coming to say something about the atmosphere in the dressing room, about the way we train or something like that. It is very positive that players are coming to me, then you know they trust you."
And that's all from Van Gaal for now. The manager certainly seems happy to have De Gea sticking around this season, but appears keen to play down expectations on Anthony Marial following his big-money move to the club.
So, join us again tomorrow to see if Manchester United can avoid a second straight defeat in the Premier League. Until then, thanks for joining me this afternoon. Goodbye.