Ireland captain Johnny Sexton on Wednesday angrily hit back at his former French neurologist, branding remarks about his concussion record "inaccurate and highly inappropriate".
The 35-year-old is going through return-to-play protocols ahead of hosting France on Sunday after taking a knock to the head in last weekend's 21-16 defeat at Wales.
In 2014, Jean-Francois Chermann recommended Sexton stop playing for 12 weeks when he was at Racing 92 due to repeated brain injuries.
Chermann told French radio station RMC that Sexton had suffered around 30 concussions during his career and said the playmaker needed to know the full risk of knocks to the head.
Sexton said he was "shocked and saddened" by the remarks.
"I think it is totally inappropriate to come out to talk to whoever it was and make remarks that are inaccurate and highly inappropriate," he said.
"I am pretty disappointed but I am used to it, it is water off a duck's back for me. However, for my mum and wife it is very upsetting, but it is the world we live in."
Later on Wednesday, Chermann said he regretted his earlier claims.
"I should not had quoted this number without any explanation and I regret the harm I could have done to a player who was my patient and I respect more than anything," he told the same broadcaster.
During a press conference earlier, Sexton queried whether Chermann had broken unwritten rules on patient-doctor confidentiality.
"Yeah I thought there was a patient doctor-confidentiality, I am pretty sure it exists globally," he said.
"I cannot get over the fact that someone thought it appropriate to say things about me that are not even accurate."
Sexton said he remained on course to captain his side at the Aviva Stadium, which is a must-win match for Andy Farrell's side, who finished third in the Six Nations last year.
The fly-half said he was on track to return to non-contact training on Thursday.
"I want to focus on this week and the return-to-play protocols. If I pass it I am able to play, if I do not then I won't be able to," he said.