Jack Clarke first played in Leeds fashion with Middlesborough but replaced half.
After 80 minutes of the game, the 18-year-old fell into the bay and was forced to hospital.
"It was taken to the hospital to see if everything was right," said Leeds coach, Marcelo Bielsa, the Yorkshire Evening Post.
Clarke should have been spiked into the catching room before being taken to hospital.
Jack Clarke, Leeds United, is in hospital after he has been ill when Middlesbrough's name is today: https://t.co/DiXuoDIWn9
– Phil Hay (@PhilHayYEP) 9 February, 2019