Referee Lee Mason made a howler in West Brom's win over Brighton ahead of his role at Bramall Lane on Sunday.
The 49-year-old will be the fourth official as he's tasked with separating Chris Wilder and Jurgen Klopp as Liverpool take on Sheffield United.
Before that though he made himself the centre of attention with a contentious decision at the Hawthorns.
He disallowed a Brighton goal having previously awarded it.
Lewis Dunk was allowed to take a quick free-kick but Mason blew the whistle before the ball hit the back of the net.
It led to several minutes of confusion before the referee eventually decided to not award the goal.
Mason's major call turned out to be the game's decisive moment as the Baggies won 1-0.
He has little time to dwell on his decision though ahead of tomorrow's clash.
Mason has previously incurred the wrath of Klopp following his role in their 1-1 draw with Fulham in December.
The Reds dropped points at Craven Cottage, but the German felt aggrieved with how the hosts scored their goal.
Bobby Decordova-Reid netted in the first-half, but Klopp felt as if Mohamed Salah was fouled in the build-up.
Andre Marriner sought help from Mason, who was that afternoon's VAR, but he decided it was "normal contact".
Klopp was clearly not in agreement and questioned how the official came to that decision.
"What exactly did Lee Mason say?" he asked.
"I am not sure what Lee Mason is doing at home but that is not ‘normal contact’ in football.
"It’s not a big deal but there is contact and it’s enough contact to get an advantage.
"It’s a foul. But we cannot change it, I only spoke about it because you asked me."
