Chelsea manager Antonio Conte believes the VAR system needs to be tinkered with.
Blues utility Willian was booked for diving in extra-time during the penalty shootout win over Norwich City on Wednesday night. Replays showed contact had been made with the Brazilian, and the Italian remonstrated about the indicent with the officials after the match.
"We need to improve if we want to use this new system," the boss said.
"There was a very clear situation with Willian at the start of extra-time. I watched it again and this is a very clear penalty.
"The referee took the decision quickly to book Willian. It means you don't have doubt. Instead, if you want to improve this new system, you have to wait to check with the person watching the game. Then, if this person is 100 per cent sure, and says it is simulation, you go and book Willian.
"The person who was watching the game must have had a doubt. There was a kick to Willian. In this case you have to call the referee and say there is a doubt. Maybe it's not a penalty, but it's better you watch the situation because the final decision is for the referee on the pitch. Otherwise we have another referee and this is not right.
"In Italy, before using this new system, they tried and tried it. When you introduce a new system, you need a bit of time before finding the best way of using it. It is not right if the referee doesn't go to watch a doubtful situation, because the final decision is for the referee on the pitch.
"This is my opinion to help the new system. In Italy we have been using this system for six months and I think you can reduce a lot of the referees' mistakes.
"I like to accept the referee's decision,' Conte added. 'But if we want to use a new system, I can't accept a big mistake. The Willian penalty was a big, big mistake, not of the referee on the pitch but the one watching on the TV.
"I hope it wasn't a referee because if you don't see this when you are watching on TV, maybe it will be impossible to see this type of situation when you are on the pitch."
