World Rugby has noted its "disappointment" that Northampton Saints failed to properly follow concussion protocols following a head injury sustained by George North in a game against Leicester Tigers.
Wales winger North has a well-documented history of suffering blows to the head, but he was allowed to return to play in the Premiership match on December 3 despite seemingly appearing to lose consciousness.
North underwent a Head Injury Assessment and Saints' medical team later admitted that he should not have been permitted to return to the pitch.
A Concussion Management Review Group, set up by Premiership Rugby and the Rugby Football Union (RFU), ruled that North should not have played on, but opted against taking any action against the club or individuals.
World Rugby stated that it would seek answers from the RFU and, having concluded a collaborative review, the governing body claims more should have been done - particularly given North's injury history - but recognised that steps have since been taken to ensure there will be no repeat failure to follow protocol.
A statement read: "World Rugby recognises the actions taken by the RFU and PRL (Premiership Rugby Limited) as appropriate in order to re-emphasise the protocols and are encouraged by the renewed efforts.
"Firstly, in the setting up of the Independent Untoward Incident Review Committee and, secondly, in the subsequent action taken since the publication of the independent review committee's findings to mitigate the risk of a repeat failing.
"While it is impossible to completely remove the risk of error, World Rugby remains disappointed that there was a failure in this case to identify and manage the injury appropriately, in particular considering North's medical history.
"Despite the failing by the club to correctly apply World Rugby's head-injury management protocols, World Rugby has recognised that the RFU and PRL acted swiftly and appropriately to implement measures with Northampton Saints and other clubs to reduce the probability of future non-compliance."