Alavés coach Luis Garcia Plaza said Endrick should have been sent off in Real Madrid's 3-2 LaLiga win on Tuesday, after the teenage forward appeared to strike defender Santiago Mouriño with his knee in an off-the-ball challenge.
Madrid led 3-0 in the game at the Santiago Bernabeu thanks to goals from Lucas Vázquez, Kylian Mbappé and Rodrygo Goes, before two late Alavés goals in two minutes made for a nervous finale.
Endrick was shown a yellow card for the clash with Mouriño, which occurred as the two players were jostling inside the penalty area.
"It's a red card," Garcia Plaza -- who had a heated discussion with Madrid counterpart Carlo Ancelotti on the full-time whistle -- said in his post-match news conference. "We should have played the last 10 minutes against 10 men.
"It's a clear red, nobody can say it wasn't. If the referee didn't see it, that's what the VAR is for. Maybe they got more yellows than they should have, but for for Endrick, it's a red."
Ancelotti said he couldn't comment. "I can't give my opinion, I didn't see it, and I haven't seen a reply," the Madrid coach said.
A club source told ESPN that Endrick would be spoken to about the incident to avoid repetition in future, although they cited his youth and energy as mitigating factors.
Ancelotti added that Madrid must avoid picking up so many yellow cards for dissent, after Federico Valverde, Vinicius Junior and Luka Modric were all booked for arguing with the referee.
"The rules have changed, and we have to get used to it," Ancelotti said. "We have to stop.
"It's not fair or unfair, we have to adapt."
Mbappé was substituted in the 80th minute, with Madrid set to face local rivals Atletico Madrid in the derby on Sunday, but Ancelotti said he wasn't concerned about the star forward's fitness.
"He's fine, he got a knock and he asked to be subbed to avoid any problems," Ancelotti said. "He's doing well. The team played well, using the ball, looking for chances, transitions, throughballs.
"The team is improving and that's good for us, we have a demanding fixture list, but we've done well since the break and want to carry on on Sunday in a demanding game."