Police Scotland have opened an investigation after assistant referee Calum Spence was struck with a missile during Rangers' 1-0 defeat at Livingston.
The Scottish Premiership clash at the Tony Macaroni Arena was held up for several minutes after Spence was struck on the back of his head by what appeared to be a coin.
The incident occurred around 15 minutes into the second half when an object was thrown from the East Stand housing the travelling Rangers support.
Spence had to be treated by Livingston physio Andy MacKenzie after sustaining a wound to the back of his head - although he was able to continue and see out the match, which Gary Holt's side won 1-0 thanks to a Dolly Menga winner.
Police Scotland have now confirmed they are looking into the incident and have appealed for information. No arrests have yet been made.
Rangers say they are liaising with Livingston and will try to identify the perpetrator once they have obtained footage of the incident. Livingston are also looking at footage and say they will pass any relevant information on to the police.
Sky Sports News understands the incident will be included in the referee's report and the SPFL may take action after reviewing the match delegate's report.
After the match, Rangers manager Steven Gerrard condemned the ugly scenes. He said: "I don't think that belongs in football, does it? I think we all know that's not right. He's trying to do a job, so that's not right."
Scottish FA chief executive Ian Maxwell condemned the "primitive act" but praised both clubs for their reactions to the incident.
"This kind of primitive act - whether something is thrown at players, staff or officials - should be driven out of the game," Maxwell said. "We all have a responsibility to behave in a responsible manner and respect the game we all love.
"At a time when there is so much to be positive about with regards to Scottish football, hopefully this is a wake-up call for some that there are lines of basic decency that should not be crossed.
"I welcome Rangers' decisiveness in moving quickly to try to identify the individual involved. I would also like to place on record my thanks to the Livingston medical staff for their assistance on the day.
"More than anything, I would like to pay tribute to the commitment and professionalism of Calum, who dealt with everything in context and continued with his role."
Scottish FA head of referee operations, John Fleming, also called the incident a "cowardly, reckless act".
He said: "On Sunday a competitive contest between Livingston and Rangers was marred by an unsavoury incident, in what should have been a great advert for the game in this country.
"Instead I was horrified to see one of our officials, Calum Spence, have to receive medical treatment after being struck by a missile thrown by a spectator.
"It is completely unacceptable for someone contributing to the sport to be the subject of such a cowardly, reckless act. I'm sure I speak for the vast majority of people when I say that it simply cannot be tolerated."