Former Australia and Saracens fly-half Michael Lynagh is being treated at the Royal Brisbane and Women's Hospital after falling ill.
Lynagh's family have requested that no details of his condition be disclosed by the hospital.
The 48-year-old, who won the World Cup with Australia in 1991, is reported to have suffered a stroke while visiting Brisbane.
Lynagh won 72 Test caps and retired from international rugby in 1995 as the then world record points scorer with 911, a total which remains an Australian record.
An inspirational playmaker, Lynagh made his Test debut in 1984 and he was part of Australia's Grand Slam-winning team later that year.
He was vice-captain of Australia's World Cup-winning side in 1991 and scored the late winning try against Ireland in the quarter-finals.
After captaining Australia to the quarter-finals of the 1995 World Cup, Lynagh retired from international rugby and joined Saracens at the start of the professional era.
He was the club's first major signing after Nigel Wray had taken control of the club and he helped attract Philippe Sella, Francois Pienaar and Kyran Bracken to the club.
Lynagh spent two years at Saracens, guiding them to a 48-18 victory over Wasps in the 1998 Tetley Bitter Cup final and he has been enrolled in the club's Hall of Fame.