Welbeck's challenge in the penalty area on Cesc Fabregas was referred to Video Assistant Referee Neil Swarbrick by Martin Atkinson but after a lengthy delay the decision was no penalty.
Riley, general manager of the Professional Game Match Officials Limited, said: 'That is a little bit longer than we have done in training.
He told BBC Radio 5 live: "We're coming up with ideas to make that more effective".
Martin Atkinson stops play to consult with the Video Assistant Referee during the English League Cup semi-final first leg
I didn't know the VAR was actually looking at that incident.
Riley, whose career highlights included refereeing the 2002 FA Cup final and officiating at the Euro 2008 championships, also admitted spectators could be better informed as to when the technology was being deployed. "Part of the process we're going through at the moment is how we can do that really effectively".
The FA plans to trial VAR - which is already being used in the Bundesliga, Serie A and Major League Soccer - in each round of the FA Cup ahead of a potential wider introduction in English football.
"I could see him (Atkinson) talking to somebody in his ear but I got the ball clearly so I wasn't anxious". The more we do it the faster we will be.
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However, a spokesperson for the North American Aerospace Defense Command told BuzzFeed News the incident was a false alarm. Saiki says, "Clearly, government agencies are not prepared and lack the capacity to deal with emergency situations".