(CNN) The safety and health of rugby players is under intense scrutiny after George North -- one of the sport's global stars -- was knocked unconscious during a club game but was later allowed to return to the field of play.
A leading doctor, who has played international rugby, has claimed the sport's system for dealing with head injuries "isn't fit for purpose."
Dr. Barry O'Driscoll, who works in general practice in Cheshire, has criticized governing body World Rugby's concussion protocols, and says North's case exposes flaws in the assessment procedure of head injuries.
"World Rugby are totally to blame for this," O'Driscoll, who played international rugby for Ireland, told CNN's World Sport show.
O'Driscoll, who also sits on rugby and tennis anti-doping bodies, resigned from his role as World Rugby medical adviser in 2012 due to his disagreement with the in-game medical protocols surrounding concussion.
"For the last four years they have experimented with a return to play protocol for a player who has shown signs and symptoms of concussion, and this protocol is not fit for purpose," he added.
World Rugby said O'Driscoll's claims were "inaccurate" and that medical staff at his team Northampton had failed "to fully comply with the protocols."
"Contrary to his view, it was not the protocols that were at fault," a spokesperson told CNN Friday. "A number of errors of application led to this unfortunate incident, as clearly stated in the report.
"Loss of consciousness or suspected loss of consciousness should result in immediate and permanent removal under World Rugby's protocols."
Last month, World Rugby's CEO Brett Gosper echoed this message, telling CNN World Sport that "player welfare is our No. 1 priority.
"We do so much in the area of prevention, treatment, management, education around player welfare, we believe the sport has never been safer to play," he said.
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Wales international North suffered the head injury in an Aviva Premiership match -- English rugby's top club competition -- between Leicester Tigers and Northampton Saints on December 3. It was his fifth head injury in two years.
The Northampton doctors gave North a pitch-side head injury assessment (HIA) without realizing that the winger had in fact been knocked unconscious -- and should not have been allowed to continue playing.
"Such instances have happened time and again," O'Driscoll said.
"It's the second time with this player that he's been unconscious on the field and passes the protocol ... it's gone on for years now, even though they've kept changing this experiment and changing the ground of it.
"We're probably doing all we can at the moment in the light of current knowledge ... but what we're not doing right is treating them on the day of the game. When we take off a player, he's got to stay off."
A review panel ruled Wednesday that Northampton would face no sanction, but did state that North should not have been returned to the field.
World Rugby told CNN there has been a significant improvement in the way pitch-side assessments have helped deal with concussions in rugby.
It said when O'Driscoll worked within World Rugby's concussion strategy in 2012, 56% of players who were examined on the field of play and passed the assessment were later determined to have suffered a concussion.
Since the HIA introduction that year, it said, the average across the global game has dropped to 4%.
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North is one of the brightest stars in world rugby, known for his pace, power and ability to score spectacular solo tries.
The 24-year-old has already won 65 caps for Wales, scoring 27 tries. He played in every game of the British and Irish Lions' tour of Australia in 2013, scoring two tries.
However, his career has been blighted by concussion injuries.
Between November 2014 and March 2015, he suffered four blows to the head, including two in one game. The recent incident was the second time North had been knocked unconscious.
His history has raised concerns surrounding his long-term health and rugby-playing future.
After this month's game, North tweeted: "Thanks for all the messages. I am okay. I landed on my neck and was worried about it. Thanks to the medics for checking me out properly. I can't help but feel I won't be looking left or right for a few days."
In the US, the issue of concussion has become a major issue for the NFL.
In September, NFL Commissioner Roger Goodell announced an initiative intended to increase the safety of the game, specifically by preventing, diagnosing and treating head injuries.
As part of the initiative, Goodell said, the league and its 32 club owners will provide $100 million in support of engineering advancements and medical research -- in addition to the $100 million previously pledged by the league to medical and neuroscience research.
"I am worried," said O'Driscoll, referring to North. "If he was an amateur player I would do everything I possibly could to stop him. I think he's not been kept off nearly long enough with these three weeks.
"If he's left with neurological problems of any kind, he should be stopped from playing the game. If he fully recovers for some time, then I think he has to look at it, his family have to look at it, and he has to be told all the dangers he's been exposed to."
Although he has returned to training, Northampton announced that North would not be selected for Friday's game against Sale Sharks, as well as reaffirming faith in its medical staff.
"The club's management remains absolutely confident in the expertise, professionalism and commitment of our medical teams," the club website reported, "and is encouraged to see that the Concussion Management Review Group has found that the medics had nothing other than player welfare in mind during this incident."
O'Driscoll, who is the uncle of former Ireland captain Brian O'Driscoll, is not the only medical authority to disagree with the way North's injury has been handled.
Headway, the brain injury association, released a statement saying that "serious questions have to be asked regarding the protocols: Are they fit for purpose and are they being properly enforced.
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"It is essential that a safety-first approach is taken. If a concussion is suspected clubs should ensure that the principle of 'if in doubt, sit it out!' is applied."