Hull's Ryan Mason is in a stable condition after suffering a fractured skull in the defeat to Chelsea, the club has confirmed.
The midfielder was taken to St Mary's Hospital in London, where he underwent surgery on the injury.
Mason is expected to remain in hospital for the next few days.
A statement from Hull said: "Everyone at the club would like to express their sincere thanks for the excellent and swift care given to Ryan by both the Accident and Emergency department and Neurosurgery Unit at St Mary's Hospital."
The 25-year-old former Tottenham player and Gary Cahill collided in Hull's box after 14 minutes with both medical teams called to the scene as referee Neil Swarbrick stopped play.
Chelsea's centre-half swiftly returned to his feet and readied himself to play again, while Mason received treatment for around six minutes before departing on a stretcher receiving oxygen. David Meyler replaced him.
The injury led to nine minutes added time at the end of the first half, with Costa giving the Blues the lead with 90 seconds remaining.
Gareth Bale, a team-mate of Mason when the pair were at Tottenham, wrote on Twitter: "Get well soon Mase!! Thoughts are with you and your family, stay strong!!!"
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