Now the Prospect Scotland Football Referees Branch, the professional trade union for senior football referees in Scotland, has called on Hampden bosses to probe the matter.

In a statement posted on their official Twitter account, they said: “We strongly condemn the unacceptable incident at today’s game. This cannot be tolerated.

“We call on the @ScottishFA to carry out an urgent full investigation. Referees & officials are entitled to a safe workplace, free from intimidation and violence.”

Rangers security chiefs will ask their Livingston counterparts for CCTV footage in a bid to help identify the culprit behind Sunday’s incident.

The clash was held up for several minutes after Spence was struck.

He had to be treated by Lions physio Andy MacKenzie after sustaining a wound to the back of his head during the 60th-minute incident.

But he was able to continue and saw out the match, which Gary Holt’s side won thanks to a Dolly Menga strike.

Rangers chiefs are now set to contact Livingston’s security officers to offer assistance in tracking down the person responsible.

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.”

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