Ireland legend to hang up his boots
After a glittering 20-year career, the giant lock will hang up his boots at the age of 39.
Warriors' Premiership Round 21 clash with Quins is an all-important one for Alan Solomons' side, and the match on Saturday 28 April will also see the club say farewell to an icon of the sport.
O'Callaghan said: "I leave the game with a profound sense of gratitude for all that it's given me. Physically I feel I can go on but now is the right time to go.
"It's time to spend more time with the kids. A professional sportsman has to lead a selfish life, but it's not fair on my family any more for me to keep doing this while precious time ebbs away with me in one country and my family in another.
"There are a lot of people to thank for my time in the game, during which I have also made so many wonderful lifelong friends, and to each and every one of you, I’d like to say a very big thank you.
"I'd like to thank Worcester in particular for making me feel so welcome and treating me so well. I've certainly felt at home for the past three seasons and I wish the club the best of luck in the future."
O'Callaghan amassed 98 Test caps, with 94 for Ireland and four for the British & Irish Lions, while he also represented the illustrious Barbarians on two occasions.
He captained the Lions in South Africa in 2009 and featured in three consecutive World Cups for Ireland between 2003 and 2011, and won the Six Nations Grand Slam in 2009.
O'Callaghan also had a decorated 17-year spell with hometown club Munster, where he won two European Cup titles and two Celtic League titles in his 268 appearances.
He made the move across the Irish Sea to join Warriors in September 2015 at the age of 36, and quickly established himself as a key figure at Sixways.
The imposing lock played in all 22 Premiership games in his first season at the club and has since gone on to make 62 appearances in the Blue & Gold. He captained the side for the first time in January 2017 and was handed the armband for the 2017/18 campaign.
During his three-year stay at Sixways, O'Callaghan has picked up the Fans' Player of the Season award in 2017 as well as the WRSC Player of the Season award in 2016 and 2017.
Warriors Director of Rugby Solomons said: "Donncha has had a stellar rugby career. He has proved himself at the top end of the game.
"More importantly, he is a quality bloke and certainly one of the finest men I have had the privilege of coaching.
"He has made an invaluable contribution to the Club over the past three seasons and has played an important role in the development and mentoring of our young players.
"He leaves behind a wonderful legacy and by dint of who he is and what he has done, he will rightly be regarded as a legend of the game."