Celta Vigo assistant coach Ernesto Marcucci hit out at referee Juan Martinez Munuera after Iago Aspas received a second yellow card for simulation but Real Madrid's Cristiano Ronaldo was not punished for an apparently similar offence.
Madrid's 4-1 victory at Balaidos took them to within a point of the title, but Martinez Munuera's handling of a number of incidents has come under scrutiny.
Celta top scorer Aspas was booked for dissent in the first half when he felt Madrid defender Raphael Varane had handled inside the area, and got a second yellow after falling to the ground following a penalty area collision with Sergio Ramos.
Moments afterwards, Ronaldo went to ground in the Celta area, with Martinez Munuera giving a goal kick and booking home full-back Jonny for his protests.
Marcucci was sent from the dugout for complaints and told his postmatch news conference: "There was a situation where diving was punished with a yellow for Aspas, and two minutes later Cristiano is not punished.
"I was far away from the two incidents, but I understand that Cristiano should have been booked for the same thing. Iago's sending off tilted the game."
Celta were also angry that Madrid midfielder Casemiro did not receive a second yellow card for a foul.
But the Brazil international told reporters: "The first foul was a yellow, no doubt, but the second wasn't -- I tried to avoid the contact.
"I am not going to change my way of playing. In 100 games at Madrid I have never once been sent off. I always think that and remain relaxed about it. People can think what they like."
He said he understood Celta were unhappy with Martinez Munuera's performance but added: "The referee did a good job. He did not have any influence on the result."