Keighley Cougars rugby league player Danny Jones has been taken to hospital after suffering a cardiac arrest during a League 1 game at London Skolars.
London Ambulance said it sent an air ambulance and two crews "to a patient in cardiac arrest" at the ground at 15:10 BST on Sunday.
"Extensive efforts were made to resuscitate him," a spokesperson added.
The match was abandoned in the 16th minute and Welsh international Jones, 29, is receiving treatment in hospital.
The Rugby Football League confirmed in a statement that Jones was taken to hospital and added: "Our best wishes are with Danny and his family at this time."
Keighley were leading 12-6 at the New River Stadium in White Hart Lane when the match was abandoned.