The midfielder was a late substitute during a 1-1 draw with Newcastle, which saw captain [Heung-min Son](/topic/heung-min-son) bid farewell after 10 years at the club.
Shortly after Son was substituted, Maddison pulled up off the ball after attempting a challenge and immediately put his hands to his head.
Seconds later he had collapsed to the pitch in agony and remained there until he was stretchered off.