“I don’t understand VAR, I think it is only used to make decisions against Barca,” Koeman told a news conference.
Barcelona coach Ronald Koeman was fiercely critical of the referee and video assistant after his side were beaten 3-1 at home to Real Madrid in Saturday's 'Clasico' in La Liga.
Sergio Ramos was awarded a penalty midway through the second half following a pitchside VAR review when his shirt was tugged by Barca defender Clement Lenglet.
The Madrid captain scored from the spot to restore his side's lead before Luka Modric added the third, inflicting a second consecutive league defeat on the Catalans after last week's 1-0 loss at Getafe.
"I don't understand VAR, I think it is only used to make decisions against Barca," Koeman told a news conference.
"You always get shirt tugs like that in the area and I think Ramos makes a foul on Lenglet first. There's a tug of the shirt, but not enough to make him fall behind as he did... For me it's not a penalty."
Barca had two penalty appeals turned down in the match, when Lionel Messi went down from a challenge by Raphael Varane in the first half and when the ball bounced off the arm of Varane in the second.
Neither incident was reviewed by the referee on the pitchside monitor.
"We have had five matches and (VAR) has only been used to go against Barca. It's never gone our way," Koeman added.
"The decision had a big influence on the final result, because we were playing well up to the penalty. We played well, we created chances and it's difficult to understand how we lost, we didn't deserve to lose how we did."
Ramos, however, had no doubt the right decision had been made.
"I think it was a very clear penalty, he tugged my shirt when I was jumping for the ball and it's as clear as daylight. It's unfair to criticise a referee for a decision as clear as that," he said.