Former Wales captain Sam Warburton has called on World Rugby to standardise the way concussion is treated.
Warburton praised Wales and England's treatment of players after suffering blows to the head in matches.
But the two-time British and Irish Lions captain claimed the same standards are not met in France.
"France don't treat concussion seriously and they've had deaths in the last 12 months," he told the Scrum V podcast.
Warburton said Wales' decision to remove fly-half Rhys Patchell early in their 19-10 defeat by Ireland on 7 September was praiseworthy.
But Warburton, who retired in July 2018 aged 29 after repeated injury problems, added: "I'm not sure if that happens in France.
"And what I've heard from players and coaches, they don't take concussion seriously so that's where I think World Rugby do need to get into a lot of the Unions.
"I've been dealt with at Twickenham where I've been knocked out; the RFU [Rugby Football Union] dealt with me brilliantly.
"Wales I think do it brilliantly so I can say firsthand that those two have things in order - I think all the Home Nations have - but I'm not sure every other country has."
Patchell failed a head injury assessment (HIA) after a heavy collision with Ireland back row CJ Stander. The stand-off is being monitored and is expected to fly with Wales to Japan on Wednesday to take part in the Rugby World Cup.
The player suffered two concussions during the 2018-19 season playing for Scarlets.
Wales coach Warren Gatland says Wales' medical staff will be consulted over Patchell's previous head injuries and they will "see how he fares over the next couple of days".
Warburton said it was important players do not go back onto the field after failing HIA tests.
"There's something called second-impact syndrome, which is when if you get concussed and you go back on and get another concussion your chances of a fatality increase massively," added Warburton.
He said Wales' move in keeping Patchell off was "because he's had a concussion - it's not with the World Cup in sight, it's for the player's safety".
Four players - two amateurs and two professional - died in separate incidents in France between May 2018 and January 2019
However, not all of those were concussion related, with Nicolas Chauvin suffering a broken neck and another - Louis Fajfrowski - collapsing and dying after being struck in the chest.
An investigation ruled his death was caused by commotio cordis. His heart stopped because he was hit in the chest at a vulnerable moment in the cardiac cycle.
Two amateur players, Nathan Soyeux, 23, and Adrien Descrulhes, 17, died after taking blows to the head.
The French Rugby Federation (FFR) has formed a global forum alongside World Rugby and has proposed a change to rugby's tackle laws forcing players to tackle opponents below the chest.
The FFR has been asked to comment.