Emergency services were called shortly after 10am on Friday to treat the player at a hotel on the Ile de Re in La Rochelle, where the Lions had been staying since Tuesday. Attempts to resuscitate the player, who was in cardio-respiratory arrest, were unsuccessful, according to French reports.
The death has thrown the team's immediate schedule into uncertainty. The European Champions Cup match scheduled for Saturday against local side La Rochelle is in doubt, and two United Rugby Championship fixtures the Lions are due to play in Scotland over the next fortnight are also affected.
South Africa Rugby officials confirmed the player's identity has not been announced while the team contacts his family in South Africa. The Lions did not respond to requests for comment. European Professional Club Rugby said it had not yet made a decision on the La Rochelle fixture and would consult the Lions.
The tragedy draws a grim parallel to the death of Anthony Foley, the former Munster coach, who died in a Paris hotel exactly ten years ago to the day ahead of a Heineken Cup match against Racing 92, then coached by Ronan O'Gara. O'Gara now coaches La Rochelle, and according to Irish media, he visited the Lions at their hotel on Friday to offer his condolences.