Los Blancos began their tour of the USA with a 1-0 defeat to AC Milan, before they fell to another loss in Saturday's El Clasico meeting at the MetLife Stadium.
Nico Paz's 82nd-minute effort failed to spark a late fightback, as Pau Victor's brace proved enough to condemn Real Madrid to a narrow 2-1 loss in the friendly clash.
Endrick, who officially joined Real Madrid this summer, played 67 minutes of the Clasico but was unable to make a significant impression on proceedings.
Courtois had a good view of his teammate's performance after playing the full duration of Saturday's match in East Rutherford.
Courtois offers Endrick advice
Speaking to reporters after the game, the Belgium international compared the Brazilian youngster to his former Real Madrid and Chelsea teammate Eden Hazard, but offered a word of warning that he needs to remain "calm" despite the high expectations on his shoulders.
"He is not very tall, but he is very strong in his legs," Courtois said. "He's a bit like Eden when I met him at Chelsea - he also had strong legs.
"You can kick him and he'll still stand. And he has a lot of strength in the shot. In training, I have seen him shoot hard.
"Above all, I think he has to calm down a little bit. I don't know if he's a little nervous, but he's going to get better and better."
Courtois unconcerned by Clasico defeat
Although Real Madrid would have been disappointed to lose to their rivals, Courtois was keen to reinforce the fact that it is only pre-season and both sides were without several key players.
"It's pre-season, we are working and obviously there are things that we can perhaps improve," Courtois said. "But in the end, we are with those who are here and so are they.
"In the end, it is a friendly that does not give much more than perhaps the prestige of the preseason, of winning this match. I think we had chances to do more. They may [have had chances to do more] also and in the end, the result is what it is."
Courtois will go up against his former club in Tuesday's friendly with Chelsea, before Real Madrid turn their focus on the European Super Cup clash against Atalanta BC on August 14.