Spurs followed protocol after Vertonghen injury - Pochettino

The defender has since been given the all-clear by Spurs, who say he has not suffered a concussion, and walked unaided out of the Tottenham Hotspur Stadium after his side lost the first leg 1-0 on Tuesday.

But questions remain over the first-half incident against Vertonghen's former club Ajax, when a clash of heads with teammate Toby Alderweireld left him bloodied and in need of treatment.

Dawn Astle, daughter of former West Brom and England forward Jeff, who died in 2002 of a degenerative brain disease, expressed her shock on Twitter accompanied with images of a bloodied Vertonghen laying on the pitch, saying: "I literally cannot believe what I've just seen."

Brain injury charity Headway called for football's authorities to introduce "temporary concussion substitutions" to allow medical staff to make proper assessments of injured players.

Referee Antonio Mateu Lahoz spoke to Spurs' medical staff before allowing the defender to return to the field, only for the 32-year-old to quickly go off again.

Tottenham boss Pochettino had to put his arm around Vertonghen to help keep the groggy defender up before he was carried away after appearing to retch by the touchline.

A Spurs official told Britiain's Press Association after the match that the defender was fine and had passed all concussion tests, although Vertonghen will have more assessments over the coming days.

Pochettino said: "I wasn’t involved. That was the doctor's decision. I think (the health of the player) is so important, the protocol is there and our medical staff follow the protocol."

The Spurs manager said the medical staff would always be the "boss" in such situations and that he would have made the change sooner had he been instructed to.

Asked after the match how Vertonghen was, Pochettino said: "Now is OK, now is good. He was walking away, was more relaxed. Hope it is not a big issue."

UEFA implemented new concussion procedures across all of its competitions following approval by the Executive Committee in September 2014.

Champions League regulations state: "Any player suffering a head injury that requires assessment for potential concussion will only be allowed to continue playing after the assessment, on specific confirmation by the team doctor to the referee of the player's fitness to do so."

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.

Lloris, in goal on Tuesday, could not stop Donny van de Beek's 15th-minute effort in north London, where David Neres hit the post late on as Spurs pushed for an equaliser.

Luke Griggs, spokesman for Headway, said: "We believe the time has come for football to introduce temporary concussion substitutions that would allow for longer off-pitch assessments to be conducted."

Griggs added: "It is hugely disappointing that we are once again talking about concussion rather than the game itself.

"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."