London - Former Australian captain James Horwill announced on Monday he is to retire at the end of the season.
The 62-time capped lock, who turns 34 next month, could yet bow out on a high note by skippering his English Premiership side Harlequins to the title.
Horwill - who led out Australia 16 times including during the 2011 World Cup campaign - said his body had reached its limit after 13 years of top level rugby.
"I have given this great game everything I have, and I feel I can no longer give what is needed to play at this elite level," he said in a club statement.
"Rugby has been a big part of my life for many years; never in my wildest dreams would I have envisaged the incredible journey it has taken me on.
"Winning the Super Rugby title (2011) at the Reds and being asked to captain my country are just some of the moments I will look back and cherish for a lifetime."
Paul Gustard, Harlequins head of rugby, hailed Horwill as a "warrior".
"James is a true warrior of our great game; the ultimate professional and someone you always want on your side," said Gustard.
"It's been an honour and a pleasure to work alongside him at Harlequins.
"His resilience and character have made him the role model he is today and will continue to be long after his retirement."
Horwill made his professional debut in 2006 for the Queensland Reds and earned international recognition in 2007, making his Test debut against Fiji.
Despite his youth, Horwill was handed the Reds captaincy in 2008 and the second-row forward led the franchise to its first professional title, beating the Crusaders in the then-Super 15 final.
Horwill joined Harlequins in 2015 and was named club captain ahead of the 2017/18 season. His final home appearance will be on May 3 against Leicester although he will hope his side make it to the playoffs.
They are presently in the fourth and final spot, three points better off than Wasps with three matches of the regular season remaining.