De Gea was voted United's Player of the Season last term and has followed that up with a string of impressive performances in the current campaign, helping the club to third in the Premier League.
With just 18 months to run on the Spaniard's contract, Van Gaal has possibly brought former Barcelona number one Valdes to the club as a contingency plan, with reports in Spain and the UK suggesting Real Madrid will target De Gea as a replacement for Iker Casillas.
But Van Gaal is not concerned by the rumours, and remains convinced De Gea will extend his deal with the 20-time English champions.
The Dutchman said: "I think there is no problem for him to sign. It's the same as other players. You can ask other players and I can answer the same.
"It's always like that. When you are a fixed line-up player, then probably you are the best and then the manager is very happy that a player that is fixed in the line-up will stay.
"It's always like that."
Van Gaal gave Valdes his Barcelona debut in August 2002, the goalkeeper going on to win six La Liga titles and three UEFA Champions League medals.
The Old Trafford boss does not expect Vades to accept playing second fiddle to De Gea, but believes the signing was crucial as he looks to return United to their lofty perch in world football.
"Nobody is happy to be number two," Van Gaal added.
"He has to have the ambition to beat De Gea. That will be very hard for him but my ambition is to have the best players who can co-operate and make us the best team in the world."
