Paris - Ireland warhorse Johnny Sexton insists he is fit for his country's Six Nations clash against France on Saturday, but he must overcome worries about his future after a series of head injuries.
A French brain specialist who forced Sexton onto the sidelines for three months has backed the Irish fly-half's claims to be safe to play.
But Jean-Francois Chermann also said he had once warned him to avoid repeat concussions or risk his career.
The 30-year-old Sexton, one of the most influential figures in Ireland's double Six Nations triumphs, saved his side last weekend with a penalty kick that rescued a 16-16 draw against Wales.
However, he was clearly in pain when he left the field with a shoulder injury in the Dublin clash.
In naming Sexton for the team to play in Paris on Saturday, coach Joe Schmidt said that the fly-half is "pretty fit".
"I'm okay now, I just got a bang on top of the head and it just compressed my neck a little bit," said Sexton, who kicked 11 points against Wales.
"I've turned around pretty quick. But I'm fit to go and really looking forward to it."
Sexton, whose high tackling style makes him vulnerable to head shocks, suffered his latest big scare just before the Six Nations started when playing for Leinster against Wasps.
As he was being treated, Wasps attacked and Sexton leaped up to help his defence. He later left the field though.
Leinster said at first it was a suspected concussion case and then changed their minds.
The events have heightened fears about the player's future.
Sexton was forced to miss three months of rugby in late 2014 and early 2015 after suffering four concussions in a year playing for Racing 92 in France and for Ireland.
Irish Independent rugby commentator George Hook said last week that Sexton should consider quitting after the latest blow.
"Sexton's history in this area is deeply worrying for everybody concerned about the well-being of this young man," Hook wrote.
"What price is the 30-year-old prepared to put on his future health? How many more blows to the head is he prepared to take in the name of professional sport?
"Maybe it's time he gave serious consideration to cashing in his insurance policy and leaving rugby with his faculties still intact."
Chermann, a French neurologist who specialises in sporting injuries, said that Sexton should be more worried about suffering concussions in quick succession than the number of blows to the head.
Chermann signed Sexton off for three months in late 2014.
"After this period of rest and gradual return, everything went well and he did not have a new concession," Chermann said.
"At the time, I told him we should be more worried if he had a concussion in the three months after his return and he should then consider stop playing rugby."
The damage is more likely to last a long time if the two blows are suffered shortly after each other, according to the specialist.
Sexton's playing style puts him at risk. Grenoble's Irish coach Bernard Jackman said that opposing teams often target Ireland's number 10 because of their defensive style trying to get the ball out to the wings.
Sexton left the key World Cup clash against France last November after just 28 minutes.
Last weekend, Welsh ironmen Jamie Roberts and Toby Faletau singled out Sexton.
Irish legend Brian O'Driscoll said Sexton should change his tackling style so he does not go in head first.
He could also be given a wider defensive position. But Jackman said Sexton is "too proud" for such a move.
"He is not the kind of player to hide. He wants to be a leader in defence, showing the example," Jackman said.