The tighthead is stable but remains in intensive care while his recovery will take a long time, thus ending his playing career.
"Uini Atonio was admitted yesterday to the La Rochelle Hospital Centre following a suspected heart problem. Medical examinations confirmed a cardiac event. His condition is now stable, and he remains in intensive care under observation," La Rochelle's statement read.
"Following his hospitalisation, Uini will have to undergo a long period of recovery. It is now established that he will not be able to continue his playing career.
"Uini holds a special place in the history and in the heart of our Club. This news deeply saddens us. The entire Club wishes to express its unwavering and total support to him and his family during this difficult time."
France squad: Fabien Galthie brutally axes three stars for Six Nations title defence
Atonio was born and raised in New Zealand, but he played the entirety of his professional career in France after joining La Rochelle in 2011.
The prop played for Samoa at age-grade level but, after qualifying under World Rugby's residency laws, he decided to commit to France.
He made his Test debut in 2014 and went on to earn over 60 caps for the national team, particularly becoming a key part of the set-up under Fabien Galthie.
Atonio has been considered one of the best tightheads in the world over the past few years, with his size and power making him an outstanding scrummager and also a big carrier in the loose.
The 35-year-old initially retired from Test rugby after the 2023 Rugby World Cup quarter-final defeat to the Springboks but was convinced to continue by France head coach Galthie, winning a Six Nations title in 2025.
Despite injury disrupting his 2025/26 season, he was called up to the Test squad for the upcoming annual international tournament, but this incident has been forced him to retire with his final match coming against Harlequins in the Investec Champions Cup.
Bundee Aki has been hit with a suspension for verbal abuse and disrespect towards match officials, resulting in a lengthy suspension that will see him miss a large part of the upcoming Six Nations.
Ireland's Six Nations preparations have been rocked by the revelation that Bundee Aki didn't fly to Portugal with the squad on Tuesday due to disciplinary reasons.
Springbok head coach Rassie Erasmus says World Rugby is taking the prospect of a globally aligned rugby calendar very seriously.
Ireland have been forced into a pair of squad changes ahead of their Six Nations preparations, with injuries prompting alterations before the team departs for a training camp in Portugal.
