Anthony Martial played on after suffering a head injury in Manchester United's Premier League defeat to Watford and brain injury charity Headway have called for a review on concussion protocols in football.
A clash of heads with Daryl Janmaat in the 26th minute of Sunday's match at Vicarage Road left the Dutchman and Martial requiring medical attention.
Both played on, but a challenge eight minutes later left the United forward looking groggy as he made his way off when being replaced by Ashley Young.
The Premier League introduced new rules that included the requirement of a 'tunnel doctor' to support team medics in identifying suspected concussions and assessing their fitness to continue playing.
However, Headway believes a further review of concussion protocols are required following Sunday's scenes.
"Headway welcomed the strengthening of football's approach to concussion when these new rules were introduced, but serious questions now have to be asked about whether they are being fully implemented," said charity spokesperson Luke Griggs.
"The rules state that if a concussion is even suspected the player should be removed and not allowed to return to the game. This is a vital detail as concussion can be notoriously difficult to diagnose on the spot - particularly on the pitch with doctors under intense pressure to make big decisions that could influence matches.
"But it's vital that a safety-first approach is taken. Too often over the course of the past few seasons we have seen players return to games following a head injury only to be substituted a short time later showing more obvious signs of concussion.
"The danger is that period between the initial injury and the substitution. If the concussed player receives a secondary blow to the head in that time, the damage to their brain could be increased significantly.
"Elite-level football has to set a better example for the millions of youngsters around the world who take their lead from their idols. It must ensure that the principle of 'if in doubt, sit it out!' is applied in all cases of suspected concussion.
"We would like to see an independent review of the way in which professional football in this country is implementing its own concussion protocols in order to reduce the risk to not just professional athletes, but also to youngsters and amateurs who do not have doctors on the side of the pitch to provide medical support and advice."