Huddersfield Giants player Ronan Costello is in a critical condition at Leeds General Infirmary after being hurt in an Under-19s game on Saturday.
The match against Salford was abandoned after the 17-year-old centre was taken to hospital.
"The club respectfully asks that all supporters respect the wish for privacy and sensitivity for the family at such a difficult time," a statement said.
England second row Brett Ferres tweeted a message of support for the teenager.
"Keep fighting Ronan Costello, just shows the dangers of our great sport," said the 30-year-old former Huddersfield player, now with Leeds.
After taking charge of a 10-2 Super League defeat at home to Wakefield on Sunday, Huddersfield head coach Paul Anderson added: "We have to put all our prayers and hopes into him getting well."