Manchester United striker Lukaku went up for a header with Wesley Hoedt after just nine minutes.
The Belgian received a blow to the back of the head after winning the ball.
He received treatment from medical staff on the field and was given oxygen.
Lukaku was eventually stretchered down the Old Trafford tunnel as fans from both sides gave him a standing ovation.
He was taken off as a precaution.
An ambulance is understood to be on stand by.
Lukaku had already missed one chance in the day’s late kick off as United try to recover from three games without a win.
Manager Jose Mourinho brought on Marcus Rashford as his replacement.
There were six minutes of injury time at the end of the first half.
Take a look through the gallery above to reveal the snaps of Romelu Lukaku’s injury at Old Trafford and make sure to check back for the latest updates.