Willie Collum was correct not to send off Aberdeen defender Slobodan Rubezic during Celtic's 6-0 victory on Sunday, insists an ex-Premier League referee.

The powerful centre-back won the ball in his aerial duel with Kyogo, however, completely flattened him in the process.

Both players required urgent medical attention after the clash of heads, with Kyogo appearing to be out cold when he hit the deck.

Collum brandished a yellow card to the Montenegrin after the situation had been dealt with. 

And former referee Gallagher reckons that was the right way to handle the incident.

"Well I don't think it's a red card," he said on Sky Sports' Ref Watch. "I don't think it's a red card at all. 

"It's unfortunate because of the clash of heads, which forces Kyogo off. It does make it worse, but I certainly don't think it's a red card. Not at all."

The Celtic star took to Instagram to reveal that he has no recollection at all of what happened. 

He said: "I don't know how long I was there, but I don't remember anything about my friends worrying about me afterwards, about walking off the pitch on my own. I don't remember anything.

"At the hospital, I was told that everything was fine and I felt that the football gods had protected me. I will never forget my gratitude and will do my best for the future."

READ MORE: Kyogo 'doesn't remember anything' about Aberdeen injury

Brendan Rodgers also revealed that the 28-year-old will not be travelling with his country on international duty.

Post-match he commented: "It was not great for him. Obviously it was a nasty blow for him so he will not travel to Japan as he will need to recover.

"The medical team will make sure he is okay. I have not seen it back but it looked a real sore one."