UEFA president Aleksander Ceferin is unsure whether video assistant referees (VARs) will be implemented into European football.
World football's governing body FIFA has used VAR in both international friendlies and the Club World Cup this year.
Kashima Antlers became the first side to be awarded a penalty by VAR in their Club World Cup semi-final win over Atletico Nacional.
But Ceferin says uncertainty over the technology will prompt a cautious approach.
"For me and UEFA, it's just an experiment at the moment," Ceferin said.
"It's not very clear and we don't know when we'll use it. Let's see what happens in the future, but it's not in our plans to use it."