Brain injury charity Headway has called for football's authorities to introduce "temporary concussion substitutions" after Tottenham defender Jan Vertonghen tried to play on with a serious-looking head injury.

Spurs' medical staff are facing questions after they allowed the Belgium defender to go back on to the pitch during their Champions League semi-final first-leg defeat to Ajax after lengthy treatment following a collision with team-mate Toby Alderweireld.

Vertonghen, whose face was bloodied, lasted a matter of seconds after his reintroduction before going down again, where he retched on the side of the pitch and had to be helped down the tunnel, unable to walk unaided.

The Premier League club later said that Vertonghen had passed all concussions tests and was fine, but the charity insists rolling substitutes would allow medical staff to make proper assessments of injured players.

Luke Griggs, spokesperson for Headway, said in a statement released to Press Association Sport: "We believe the time has come for football to introduce temporary concussion substitutions that would allow for longer off-pitch assessments to be conducted.

"Concussion is notoriously difficult to diagnose. The symptoms may be hidden and require the individual to be honest about how they're feeling, while they can also be delayed in their presentation.

"Assessing a player for three minutes – or even five, as was the case with Jan Vertonghen – does not allow for medical staff to make a reliable diagnosis, particularly when this is conducted on the pitch under the gaze of tens of thousands of fans eager for the game to resume.

"The pressure on club medical staff is enormous and unfair, particularly in such high-stakes games such as a Champions League semi-final."

Dawn Astle, daughter of former West Brom player Jeff Astle, daughter of former West Brom and England forward Jeff who died in 2002 of a degenerative brain disease, responded to the injury by tweeting: "I literally cannot believe what I've just seen."

Referee Antonio Mateu Lahoz made a point of asking several times whether Vertonghen was fit to carry on and got a positive answer.

Griggs also believes that the assessment and decision whether a player can continue should be made by an independent doctor.

"In addition, independent doctors with expertise in concussion and head injuries should make the ultimate decision as to whether or not a player is fit to continue," he added.

"Not every head injury will result in a concussion. But allowing players to continue while showing clear signs of discomfort following a head injury is contrary to the 'if in doubt, sit it out' principle at the heart of all effective concussion protocols."

Tottenham boss Mauricio Pochettino insisted he played no part in the decision to allow his defender to play on.

The Argentinian said: "I wasn't involved. I wasn't involved. It was the doctor's decision.

"I think it's so important, the rules and the protocol are there and our medical staff follow the protocol.

"I was never involved. The decision was the doctor and the referee asked."

Tottenham were criticised in November 2013 after goalkeeper Hugo Lloris was allowed to remain on the pitch against Everton after being knocked out in a collision with Romelu Lukaku's knee and initially being unable to remember where he was.