Willie Collum will not referee the Scottish Cup semi-final between Celtic and Rangers due to a late injury.
The whistler was set to take charge of the powderkeg fixture but has pulled out right before kick-off due to a calf strain.
Fourth official Don Robertson will now referee the match having stepped into the role just before kick-off. Collum had filled in as the fourth official at kick-off.
However, John Beaton was called up to serve as the fourth official at Hampden after Collum's injury problem.
Daniel McFarlane and Dougie Potter are the assistant referees for the match with Steven McLean in the VAR room alongside Frank Connor.
