PSV Eindhoven talent Gakpo, Steven Bergwijn and Vincent Janssen were preferred to Depay in the starting XI, with the Barcelona attacker brought on in the 62nd minute for the latter.
”We had agreed before the game that he would play about half an hour,” van Gaal told reporters.
“With Ecuador, he will want to play, but I have to assess his form after this game. I never thought we would lose and, with the entry of Depay, I wanted to have more chances to score. He is a player who can make the difference.”
Van Gaal praised Gakpo, who has been linked with Manchester United. The young attacker got his head to Frenkie de Jong’s lofted ball before Senegal keeper Edouard Mendy for the opening goal in the 84th minute.
“Gakpo was decisive, I left him inside because he knows how to score goals and is very agile,” he said.
Van Gaal also praised goalkeeper Andries Noppert, who made his international debut in the game. The 28-year-old Heerenveen stopper made a few key saves to keep Senegal at bay.
“Senegal had three chances, but we have a goalkeeper who knows his stuff between the posts,” van Gaal said.
“We didn’t play very well, too many times, we gave them the ball and the chance to score.
“We had to be more compact. We can only improve, there was probably some tension between the players.”