South Sydney captain Sam Burgess has announced his immediate retirement in a heartfelt letter to fans.

In what is a sad end to one of the most decorated careers of the modern era, a shoulder injury Burgess suffered earlier in the year has brought a premature end to his playing days.

"I have loved absolutely every minute; the highs, the lows; the grand final; coming home; my injuries; my dates with the judiciary. It really has been a fantastic ride,": he wrote in his letter to Bunnies fans.

"This decision was one of the hardest decisions I’ve had to make in my life, however the decision was out of my hands essentially. I am no longer able to be myself day in, day out on the training field and consequently the playing field.

"I will not be playing in the NRL next season. My time has come to an end. I’m excited for my next chapter in life whatever that may be."

Burgess seemed at ease with his decision, paying tribute to his teammates and Rabbitohs co-owner Russell Crowe.

"I’d like to encourage everyone to smile as they read this. Let’s all remember what we have done together as a club over the past decade rather than what’s not to be in the coming years," the 30-year-old English forward wrote.

"We have some amazing young men at the club and it’s in safe hands. I will stay close and help grow the club continually in any way I can. To my teammates and coaches along the way, I’d like to thank you all for being supportive and great men. I’ve learnt so much in my 10 years here.

The best of Burgess

"From the young boys all the way through to ‘the fossil’ John Sutton. I value each friendship created and they’ll last a lifetime.

"To Russell - for making all this happen initially - I’ll be forever indebted to you. Your passion is infectious.

"My family have been by my side the whole way, on and off the field. I love you all so much. Maybe I’ll come and watch a game in The Burrow next year. You truly are the heartbeat of the club.

"I’m sure you’ll agree with me, the spirit of South Sydney is alive and will live long after me. It will always be a huge part of my heart. Just like it is yours."

Rabbitohs coach Wayne Bennett paid tribute to the Clive Churchill Medal winner from the 2014 grand final success by praising the effect he has had on him in recent seasons with England and South Sydney.

"I was lucky enough to coach Sam in the All Stars game in 2010. I’d had heard so much about this Englishman that I had to see him for myself," Bennett said.

"Then I had the opportunity to coach him with England and I was hoping to coach him again this year with Great Britain. He was one of the drawcards for me in coming to coach at South Sydney.

"His leadership and capabilities on the field match the man he is off it. I thought it was a real blow to the game when he left to play rugby union but I’m glad he saw the light and came back."

My time has come to an end. I’m excited for my next chapter in life whatever that may be. Sam Burgess

South Sydney will now work with the NRL to determine how much, if any, of his four-year deal (believed to be worth around $1 million a year) will count in the salary cap.

In 2019, Burgess was a shadow of the player he once was as he battled through the pain of a shoulder injury that dogged him throughout the majority of the season.

NRL chief executive Todd Greenberg said Burgess has been a "true champion of our game".

"He inspired so many players from the UK to want to play in the NRL. Our competition is stronger today because of Sam’s influence," Greenberg said.

Looking back at the 2014 grand final

His heroics in the 2014 grand final will forever remain in NRL folklore, as will his status as a South Sydney legend."

It comes after a NewsCorp report that Brisbane Broncos veteran Matt Gillett could also be forced into retirement as he battles his own shoulder problems.

It's expected South Sydney will enter the market place for a high-profile replacement, pending an NRL decision on the salary cap implications of Burgess' retirement.

Tom Burgess reacts to brother Sam's sudden retirement

Brisbane's David Fifita is a genuine option for 2021, however the Rabbitohs could go after Ryan Matterson given his ugly break-up with the Wests Tigers.

Fox Sports has reported St George Illawarra's Tyson Frizell has been mentioned as a potential target given the uncertainty about his future at the Dragons.

"There will obviously be questions about what Sam’s retirement means for South Sydney’s 2020 salary cap and beyond," Greenberg said.

"There are rules surrounding these matters and it’s important we take our time to work through the facts with South Sydney in a considered and methodical manner."