The 27-year-old was named the Red Devils' Player of the Year this season for a fourth time after keeping 18 clean sheets in the Premier League.
Despite a rare lapse in concentration during Spain's 1-1 draw with Switzerland on Sunday evening, allowing Ricardo Rodriguez to convert from close range after a Stephan Lichtsteiner shot slipped through his grasp, De Gea will be La Roja's number one at the World Cup.
Del Bosque, who spent eight years managing Spain until Euro 2016, believes that his nation are in safe hands this summer.
"David is a really complete keeper," he told Omnisport. "He plays well with his feet, which is important. He is improving and will be better.
"He's been playing for five or six years in Manchester, that's a huge learning experience, same with the national squad."