Problems with the video technology system in use at the Confederations Cup must be solved if it is to be employed at the 2018 World Cup, FIFA says.
Law-making body International Football Association Board will decide next March if video assistant referees will be used at next year’s event in Russia.
During the 12 Confederations Cup group games, the system helped correct six “game-changing decisions”, said FIFA’s head referee Massimo Busacca.
“We have really good results,” he said.
“But many aspects should be improved.”
Busacca said officials had ruled correctly on a further 29 “major incidents” after referring to the video replay team, and that FIFA was keen to convince member nations to use the technology (VAR).
Spectators, players and team officials have complained of being left confused while officials have been making decisions with the help of VAR.
Busacca said referees needed more training in how and when to use the technology, and added the system could be sped up.
Last week, FIFA President Gianni Infantino described the system as “the future of football”.
Its most recent and most confusing  use came during Germany’s 3-1 victory over Cameroon last Sunday.
First, Colombian referee Wilmar Roldan showed a yellow card to Cameroon captain Sebastien Siani in a case of mistaken identity.
It was actually Ernest Mabouka who fouled Germany’s Emre Can, but after Roldan consulted the VAR, he upgraded the yellow he had shown Siani to a red.
After a further referral to VAR, and much confusion on the pitch, Roldan rectified his mistake and Mabouka was sent off.
Cameroon boss Hugo Broos said of the decision: “I didn’t understand it and I still don’t understand it now.”