Swimming star Leon Marchand pulled out of the French nationals on Tuesday with a leg muscle issue just weeks before the European Championships.
During the 200m breaststroke heats on Monday, Marchand felt sharp pain in the adductor muscle of his right leg, his team said.
"To avoid any aggravation and to protect his health, Leon has decided in consultation with his technical and medical staff not to continue competing," a team statement added.
It was not specified whether the injury would jeopardise his participation in the European Championships from August 10–16, a competition which would mark his return to Paris two years after his triumph at the 2024 Olympics.
Early on Monday, the 24-year-old had placed a surprise third in his 200m breaststroke heat in 2min 16.16sec.
After swimming the first part of the race at a good pace, Marchand visibly eased with television footage showing him clutching his right thigh at the end of the race.
The four-time Olympic gold medallist and seven-time world champion had gotten off to a flying start to the French championships, clocking the fifth-fastest time in history in the 400m individual medley final on Saturday.
The withdrawal does not jeopardise his qualification for Europeans having already secured his spot with his performance on Saturday.
He could still be selected for other events if all qualification quotas are not filled by the end of the competition in Saint-Etienne and provided he is fit.