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".
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."
An Ifab report last month said that the VAR system has been accurate in 98.9% of decisions so far during its two-year worldwide trial.
In England, VAR has been used in selected matches in the FA Cup. It has also been used in the Carabao Cup, where it featured in Sunday's final, with Arsenal manager Arsene Wenger unhappy that it did not rule out Manchester City's second goal.
Fifa president Gianni Infantino said on Monday that he continued to support the use of the system, which has been trialled across 20 competitions over the past two years, at this summer's World Cup finals in Russia.
He said: "If we, or I, can do something to make sure that the World Cup is not decided by a referee's mistakes, then I think it's our duty to do it."