Warriors doctor John Mayhew is in an induced coma in an Auckland hospital after suffering a cardiac arrest as a result of a heart problem.
Mayhew was taken to North Shore Hospital after the incident on Tuesday night, a family spokesperson said in a statement.
He was successfully resuscitated and was in a stable condition in intensive care.
The spokesperson said there would be no further comment at this stage.
NZME reported earlier that Mayhew, 61, collapsed after an exercise class.
Mayhew has worked with various sports and was invested as an Officer of the New Zealand Order of Merit last week for his services to sports medicine.
He was the All Blacks doctor for 131 Tests over 15 years and has been with the Warriors NRL club for most of the past decade.
