Devastated former Olympic champion Carolina Marin withdrew in tears from her badminton semifinal on Sunday after her right knee buckled in distressing scenes.
Marin, who won women's singles gold at the Rio 2016 Games, was on track to reach the final but collapsed midway through the second game against China's He Bingjiao.
Coaches and He rushed to her side as she lay on the ground for several minutes, clutching her leg.
She eventually got up and walked off the court then resumed wearing a support but she could barely move, losing the next two points before falling to the ground again and retiring.
Marin, the fourth seed in Paris, won the first game 21-14 and was leading 10-6 in the second before she left the court in tears before going for a medical check.
Her coach, Fernando Rivas, told reporters that he had "no words to describe what happened".
"Carolina knows that at an Olympic Games, you win or you lose," he said. "But not this way."
Marin was hot favourite for the title at the Tokyo Olympics three years ago until she suffered an anterior cruciate ligament injury just months before the event – her second ACL injury.
"She was in pain, it's a sensation that she already knew," said Rivas.
"Now we have a lesson and we need to restart and try to understand what happened."
Marin's withdrawal drew a sympathetic response from Spanish Prime Minister Pedro Sanchez on social media.
"You are and always will be a champion," he wrote on X, formerly Twitter.
"All of Spain is with you."
Her opponent He progressed to the final, where she will play South Korean world No 1 An Se-young.
A clearly uncomfortable He told reporters that she felt "very sad" about what had happened.
"She was playing perfectly well and I was very passive," said He. "I wasn't thinking about the final at all."
An beat Indonesia's Gregoria Mariska Tunjung 11-21, 21-13, 21-16 in the day's earlier semifinal.