Video assistant referees (VAR) will not be used in next season's Champions League, with the head of Uefa saying he sees "a lot of confusion", reports BBC Sport.
The International Football Association Board, which rules on the game's laws, meets on Saturday to decide whether to approve the technology permanently.
If it does, then Fifa is committed to using the system at the World Cup.
But Uefa president Aleksander Ceferin said: "Fans see the VAR screen all the time but nobody knows how it works."
He added: "We will not use it in the Champions League next season.
"For me, it might be a good project but we shouldn't rush it."