Barcelona coach Ernesto Valverde is concerned the introduction of the VAR system may interrupt football as a spectacle.
"The feeling is that video assistant referees and technology are here to help us, especially for justice in the penalty area," he told the Barça website.
"But we don't know what knock-on effects it might have.
"I wouldn't want VAR to interrupt the flow of games. The great thing about football is that it's so fast, there are so few interruptions. The referees certainly need help but this shouldn't be to the detriment of the speed of the game.
"I know everyone is hanging on what happens in the area, but in the World Cup final, France scored from a free-kick that wasn't and that decided the game. So what's more important? I don't know, because I am also waiting to see how it all works out."