Police Scotland said on Monday they are looking into alleged online racial abuse of Rangers' Colombian striker Alfredo Morelos after he scored in Sunday's 1-1 draw with Celtic.
"An investigation is under way after we received a number of complaints regarding an offensive social media post and enquiries are ongoing," Police Scotland told British media.
Rangers captain James Tavernier said all black players in the team had been abused on social media this season.
Brentford confirm signing of £13.5m Ajer from Celtic
- Rangers held to Old Firm draw by Celtic as Alfredo Morelos scores for Scottish Premiership champions
"We took a knee to send out a message but we believe that message isn't strong enough. We wanted to send out a strong message and it was an easy decision," he said.
"But I feel confident saying that all our black players have received racial abuse this season. That's from social media platforms and this is a key message to them. Action has to be taken - enough is enough."
Celtic pegged back by FC Midtjylland in UCL qualifier
Ajer completes Brentford medical ahead of £13.5m move from Celtic - reports