Northampton should not have allowed George North to continue playing after he sustained a head injury but they will not be punished, a concussion review panel announced on Wednesday.
The Wales wing, 24, was injured during an English Premiership game against Leicester on December 3, but although he appeared to have been knocked out, Saints' medical staff allowed him to play on.
A Concussion Management Review Group (CMRG) was set up to investigate the incident, the first such review since new concussion rules came into force at the beginning of the season.
It found that while there had been "sufficient evidence" to take North out of the game, the club did not "intentionally ignore the player's best interests".
"Northampton Saints medical team has accepted that North may have lost consciousness and therefore should not have returned to play," the CMRG said in a press release.
"The CMRG considered the welfare of North was always at the centre of Northampton's actions, and does not consider that the medical team (or the club) failed to complete the HIA (Head Injury Assessment) protocol nor intentionally ignored the player's best interests.
"In addition and although not a determining factor, the CMRG is aware that the player appears to have had no residual effects in the short term.
"For the above reasons the CMRG will not be imposing any sanction against the club or any of its individuals as a result of this incident."
Northampton accepted the panel's findings.
"Northampton accepts the conclusion that George should not have been allowed to return to the field of play," the club said in a statement.
"But we are pleased that the CMRG has reflected our concerns about the current technologies and processes available to medical teams when assessing concussion.
"The club believes that this is now an opportunity for the whole rugby community to reflect on the CMRG's recommendations to ensure the highest levels of player safety and well-being."
Rather than instigate disciplinary proceedings against Northampton, the CMRG, set up in partnership by the Rugby Football Union and Premiership Rugby, made nine recommendations.
They include a call for the full 13 minutes set aside for Head Injury Assessments to be used unless there is clear reason to shorten it.
The CMRG also wants team doctors to review video footage for permanent removal criteria before and after the assessment process.
North, who has a history of head injuries, has since returned to training and Saints director of rugby Jim Mallinder said earlier this week that he will play against Sale on Friday.