Liverpool have reportedly asked for audio of communication between match officials during Saturday's 2-1 defeat by Tottenham after they failed to overturn an incorrect decision to disallow a Luis Diaz goal.
The Premier League game in London was goalless at the time of the incident, in the 34th minute.
Colombia forward Diaz put the ball in the net but was wrongly flagged for offside. The video assistant referee (VAR), however, failed to overrule the decision.
Liverpool went on to suffer their first defeat of the season.
PGMOL (Professional Game Match Officials Limited), the governing body for referees, issued a statement on Saturday acknowledging a "significant error" had been made.
Liverpool put out their own statement the following day saying "sporting integrity has been undermined".
The club said they would "explore the range of options available given the clear need for escalation and resolution".
Now they are understood to have formally requested the audio of the conversation between the officials from the PGMOL.
Video assistant referee Darren England and his assistant VAR at Tottenham, Dan Cook, were stood down from duty for the rest of the weekend following the error.
England and Cook had been part of a team of officials who oversaw a fixture between Sharjah and Al Ain in the United Arab Emirates on Thursday, arriving back in the UK on Friday morning.
Requests for English officials to take charge of domestic matches overseas are made to the Football Association, with permission for officials to travel granted jointly by the FA and PGMOL.
Manchester United manager Erik ten Hag said on Monday he still had complete "trust" in referees.
"They are very professional, so they will give their best and I trust them," he told a press conference.
"Of course, the standard has to be high and it's a part of the game."
