With no VAR in operation, there were several controversial moments in the last round – not least when Manchester United’s Harry Maguire headed an injury-time winner to seal a 2-1 win against Leicester City.
Maguire appeared to be offside when Bruno Fernandes sent a free-kick towards the back post but the goal stood – and Leicester went out.
Even United boss Ruben Amorim admitted his team’s winning goal should not have stood.
However, VAR will be introduced – as planned – from the fifth round onwards., external
It will be active across all eight ties including at Deepdale, where Preston host Championship rivals Burnley on Saturday.
This will include in-stadium VAR announcements, where match officials will announce their final decision in relation to reviewed incidents to provide “improved clarity and understanding” for fans and viewers.
Semi-automated offside technology will also be used in all seven matches taking place at Premier League grounds.
It is the first time it will be used live in competitive matches in English football.
The system aims to remove some elements of human subjectivity by replacing decisions made by officials with automated ones taken by technology.
If successful, the Premier League will look to implement the technology before the end of this season.