Aberdeen defender Scott McKenna has questioned why Dominic Ball was sent off on Sunday for his part in Ryan Christie’s injury when Celtic defender Dedryck Boyata escaped sanction for a clash of heads with Gary Mackay-Steven in November’s League Cup final.

Christie was stretchered off after a six-minute delay to give him treatment and was taken immediately to hospital. It is suspected that he has a fractured cheekbone and eye socket.

Ball was shown a second yellow card for the incident by referee Craig Thomson and McKenna, Aberdeen’s captain for the day, believes that there was not much between the offence and that of the incident with Boyata earlier in the season.

HeraldScotland: Gary Mackay-Steven and Dedryck Boyata clash heads in the Betfred Cup final earlier this seasonGary Mackay-Steven and Dedryck Boyata clash heads in the Betfred Cup final earlier this season

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“I have not had a chance to watch it back and I was a bit of a distance away at the time but it was a sickening injury,” he said. “You never want to see someone get an injury like that on the pitch.

“Earlier in the season Gary Mackay-Steven got knocked out after a head injury from Dedryck Boyata and there was no action given against Boyata that time. Christie gets head knocked today and our player gets the booking. The way the two of them were handled, it could have been a bit different. Boyata stayed on the pitch but we lost a man.”

Asked if Ball was guilty of being reckless, McKenna said: “It might have been. But was Boyata reckless when he knocked Gaz out? Who knows? It just seems unfair.”

Ball was the first of two red cards shown to Aberdeen; Lewis Ferguson was dismissed in the second period for a two-footed lunge on Tom Rogic while Dons manager Derek McInnes was sent to the stand after he reacted to sectarian chants from a small section of the Celtic support.

The accusation was that Aberdeen lost their discipline on the park and McKenna accepted that there was an element of that which undermined their performance.

HeraldScotland: Scott McKenna and Dean CampbellScott McKenna and Dean Campbell

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“I think with two sending-offs, you can’t argue with that,” he said. “It is something we need to learn from. There is frustration when you are losing a game like that but there is still a way that you have to behave. I think Lewis [Ferguson] will learn from it and I think we all have to take something from it. It is frustrating but you still have to try and stay in the game.

“I don’t know what he [McInnes] did to get sent off. I have not been a manager so I don’t know what it feels like to be standing in that position and I didn’t see what he did. As a player you have to stay focused and whatever is going on with the fans then you have to let them get on with it and just try and make sure you stay on the game.”

And for McKenna the most bruising aspect of the defeat was the fact that it is as heavy a loss that Aberdeen have had against Celtic in recent seasons. There was a feeling before the game that the Pittodrie side had some conviction about their chances of causing an upset, a sense of optimism that compounded the sense of frustration in the aftermath of the defeat.

“100 per cent,” said McKenna. “What an opportunity we had. We have been good in big games in Glasgow this season. We felt good, we felt confident. We were just looking to carry that on but going down to ten men and losing a goal right before the break made it really difficult for ourselves. We still felt like we could get back into it but then when they get a second and we are down to nine men, it is very, very difficult. This is up there for me with how bad I felt last season when we lost 3-0 to Motherwell [in the semi-final]. It was the same thing that we thought we had a tremendous opportunity but on the day we had things go against us.”

HeraldScotland: Aberdeen defender Mikey Devlin trips Jonny Hayes and Celtic are awarded a penaltyAberdeen defender Mikey Devlin trips Jonny Hayes and Celtic are awarded a penalty

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James Forrest opened the scoring shortly before the break with a curling 25-yard effort effort before a second-half penalty from Odsonne Edouard and a third goal from Tom Rogic completed Celtic’s passage into the final.

And while McKenna thought the penalty was soft he admitted that there was a decision for Thomson to make.

“We should have dealt with the first ball into the box better but once Jonny goes inside and goes down he gives the ref something to think about,” he lamented. “I thought he went down a bit easily. It was maybe a wee bit soft but I haven’t seen it back yet. It was bitterly disappointing. To come here and get to the semi-final of the Scottish Cup and then go out the way that we did, it is a hard one to take.”