The concussion guidelines Sunderland have to follow and when Dennis Cirkin could return

The 20-year-old defender came off the bench and scored the equaliser at The Den, but received a hefty whack from goalkeeper George Long after heading his side level.

Cirkin was immediately substituted but was able to walk off the pitch after being knocked out.

Still, Sunderland will have to follow the FA's 'Return to Play' guidelines before the full-back can return to action.

In a professional environment, protocols state the player requires a 24-hour period of rest. If they are then symptom free, a phased return to training is allowed.

That includes a gradual increase in workload over a three-day period, before a doctor can make a decision regarding full-contact training.

Providing the player remains symptom free it is a six-day programme.

That means Cirkin will definitely miss Wednesday’s match against Fulham at the Stadium of Light, but could return for next weekend’s home match against Reading – providing he remains symptom free.

After the match at Millwall, Mowbray said: "Dennis will have to go through the concussion protocols now. He'll miss our FA Cup game. The doctors tell me that if he passes certain tests he might be able to play next weekend but we'll just have to wait and see on that one."

Before the Millwall match, Cirkin hadn’t played for Sunderland since Boxing Day due to an injury.

After the fixture, he posted a picture of his goal on social media, with the caption: ”Felt good to be back out there yesterday and help the team.”