Jose Mourinho believes referees should decide whether to call for video assistance but largely backed the VAR program after Manchester United had a goal ruled out after replay on Saturday.
United advanced to the FA Cup quarterfinals with a 2-0 win over Huddersfield, but Juan Mata's effort late in the first half was disallowed by the video assistant referee, who ruled the Spaniard's knee was offside.
England's VAR system is based in an offsite studio, which communicates to the stadium when a decision must be made. The match referee has the ultimate say after hearing the evidence on an earpiece, or he can look at a pitchside monitor, which Kevin Friend opted not to do in this case.
But Mourinho said VAR should only come in when the official on the pitch asks for help.
"It's an experimental period,'' Mourinho told BT Sport. "They have to get rid of the bad and make it perfect.
"It should be the referee's decision. Why? Because the referee wants to perform well. I don't think they're happy to make mistakes and if they have the VAR to help them make the right decision, I think the referees are probably happy with that.
"But if the VAR changes their good decisions for bad decisions, I think they're not happy with that. It was a bit frustrating because the moment I saw [referee] Kevin Friend touch his earpiece, I knew something was going to happen.
"That doubt is not the best feeling. If the decision is right, I am super happy with that because I want the truth. Sometimes it goes against me and sometimes in my team's favor. But I heard comments that maybe the linesman was right and not the studio.''
The guidelines for VAR also limits its use to "clear and obvious errors, or serious missed incidents," and Mourinho said in his postgame news conference that the Mata goal did not pass that test.
"It is amazing when the truth comes but also there are problems like what happened today which goes against the words of the protocol," Mourinho said. "In Portugal we have VAR and I follow it when I am home, I am familiar with amazing results of VAR and problems and frustrations.
"But the words of the protocol are something like a clear and obvious situation and for sure is not a clear and obvious situation, but we know it is experimental and we have to accept, but I am speaking after a 2-0 victory."
Mata said he was in favour of the use of VAR, but took issue with the several minutes it took to sort out the decision.
"I celebrated, but apparently VAR showed it was offside. I don't know. It was very tight, right?" Mata said. "The important thing was that it didn't really matter because we won anyway. But it was the first time I met Mr VAR.
"I'm up for it. I think it's needed, specifically when there is a clear decision that can change the game, like a goal, offside, red card, but hopefully it will be quicker.
"But I think it's good for football to be more fair. I scored a goal, I celebrated and when I came to the dressing room they told me that even on the TV, it wasn't very clear. If the VAR is not clear, what can you do?"
Even though the decision helped his club in that moment, Huddersfield manager David Wagner said he was against the use of VAR entirely, as it took several minutes for VAR to sort out the ruling.
"The decision went in our favor but this VAR for me kills the emotion of the game," Wagner said. "This is why I don't like it but I am not the person who makes the decision."
Information from The Associated Press was used in this report.