Chelsea manager Antonio Conte said the Video Assistant Referee (VAR) system must be improved after his side's controversial penalty shoot-out win over Norwich in their FA Cup third-round replay.
Chelsea prevailed 5-3 on penalties after a 1-1 draw, but finished the match with nine men having had three players booked for simulation, with Pedro and Alvaro Morata subsequently receiving second yellow cards, Morata for his furious response to being booked.
The decision to book Willian provoked the most controversy as he was clearly clipped by City's Timm Klose, but there was no apparent referral to the VAR, with referee Graham Scott appearing to rule Willian was already on his way down when the contact occurred.
Conte said: "I think that we need to improve if you want to use this new system. Today in this game there is a situation very clear, the situation is with Willian at the start of the first half of extra-time.
"I think the situation was very clear. I watched and this is a penalty, very clear. This is not because I'm not happy for a referee decision. The referee took quickly a decision to book Willian. It means you don't have doubts. If you do this quickly it means you don't have doubt.
"Instead, if you want to improve, it's only to try to improve this new system. You have to wait, to check with the person watching the game. Then if this person is sure 100 per cent then 'OK, this is simulation, book him'. Then book Willian.
"At least you must have a doubt because there is a kick to Willian. In this case you have to call the referee and to say there is a doubt."
After Wednesday night's win over Norwich, Chelsea will host Newcastle in the FA Cup fourth round.