Police are looking into reports threatening messages were sent to a football referee after his contact details were posted online.
John Beaton, who officiated during Rangers’ 1-0 win over Celtic last weekend, is understood to have contacted officers about abusive calls and texts he received following the match.
He has been the focus of criticism by some for decisions he made during the game at Ibrox on December 29.
In a statement on Friday, Celtic called on the Scottish Football Association to allow Mr Beaton “to explain these decisions publicly as well as any match officials involved in other similar circumstances”.
A Police Scotland spokeswoman said: “We can confirm that a complaint has been made to police regarding texts and calls received by a 36-year-old man.
“Police inquiries are ongoing into this matter.”