Mikel Merino has questioned whether Real Madrid would have had a goal disallowed for offside in the same way as Real Sociedad did during Sunday's LaLiga clash.
Adnan Januzaj thought he had cancelled out Sergio Ramos' penalty in the second half at the Reale Arena, but the goal was ruled out as Merino was judged to be blocking Thibaut Courtois' line of sight while standing offside.
Karim Benzema soon doubled Madrid's lead and, although Merino got a goal back with 10 minutes remaining, the visitors held on for a 2-1 victory.
The result lifted Madrid to the top of the table, above Barcelona by virtue of their superior head-to-head record, while Sociedad are five points adrift of the Champions League places.
Merino thought Sociedad had been harshly undone by that offside call and is not sure the assistant referee would have been so certain in his decision if the incident had happened at the other end of the pitch.
"I'm far from him [Courtois], practically five metres, he has plenty of time to see the ball," he told Movistar Plus.
"The thing is that [the assistant referee] did not hesitate for even a second in raising the flag and I don't know if in the other area he would have hesitated the same way.
"In the end, he raised it and it hurt us."
Merino felt "more annoyed than sad" after the match but remains confident in Sociedad's Champions League chase despite them having taken just one point from three games since LaLiga returned.
"We can't be sad because we gave a very good picture of ourselves and we've returned to those feelings we had before the break: playing well, having control of the ball and feeling good in defence, but we can't leave content because of how the game went," he said.
"There are lots of points left [to win] and if this team has anything it's that we don't stop believing or working. The run we had before was six, seven victories and why won't we do that again? We have the strength and the confidence to do this."