Rabbitohs great Merritt is fighting for his life in hospital after being found unresponsive on Friday, according to reports.

Merritt is understood to be on life support after being taken to Royal Prince Alfred Hospital following a negative reaction to prescribed medication.

Merritt was reportedly staying with his Aunty.

His condition was listed as serious.

Family, friends and former teammates have been notified of his condition.

The 40 year old played 237 NRL games between two long tenures at South Sydney and a short stint with Cronulla.

He scored 154 tries - the equal-12th most by any player in the competition's history, and is fourth on South's all-time list of games played for the club with 219 appearances.

The champion winger made played one State of Origin game for NSW and represented the Indigenous All Stars on three occasions.

Merritt retired in 2014.

"Nathan is in the thoughts and prayers of every Rabbitoh at the moment," South Sydney chief executive Blake Solly said on Saturday, via the Daily Telegraph.

Merritt played at the Koori Knockout on the NSW Central Coast last weekend.