Middlesbrough academy player Anthony Renton has been diagnosed with leukaemia.
The 18-year-old defender, who signed his first professional deal at the Riverside in April 2017, has been admitted to the Freeman Hospital in Newcastle for treatment.
"We were all saddened and shocked to the hear news about Anthony," said manager Garry Monk.
"He's got our full support and we'll be with him every step of the way."
A statement on the club website said: "As a club we have been right behind Anthony and the family, offering logistical and moral support and as everyone, Anthony especially, comes to terms with the situation the need for continued support from everyone is obvious."
Wolves goalkeeper Carl Ikeme, 31, was also diagnosed with leukaemia at the start of July. Wolves will host Middlesbrough on the first day of the new Championship season on 5 August.