Hull midfielder Ryan Mason was taken off on a stretcher following a clash of heads during the first half of Sunday's Premier League fixture at Stamford Bridge.
The 25-year-old former Tottenham player and Chelsea's Gary Cahill collided in Hull's box after 14 minutes.
Both medical teams rushed to the scene as referee Neil Swarbrick stopped play.
Cahill quickly returned to his feet and readied himself to return to the action.
Mason received treatment for around six minutes before departing on a stretcher, while receiving oxygen.
David Meyler replaced him.