Tottenham's Jan Vertonghen was left with blood pouring from his face following a clash of heads with teammate Toby Alderweireld during their Champions League match with Ajax, prompting questions over the concussion protocol.

Belgian defender Vertonghen suffered a gruesome cut to the bridge of his nose after a clash of heads in the coming together with his center back partner towards the end of the Champions League semi-final first leg at the Tottenham Hotspur Stadium on Tuesday.

The former Ajax player was prone on the ground for several minutes as he was attended to by Spurs' medical personnel, who did their best to wash away the blood and stem the injury but they have come under fire online for allowing the player back on the pitch, particularly when he was removed from the game minutes later after appearing unsteady on his feet and nauseous. Dizziness and nausea are two symptoms of concussion.

Vertonghen signalled to his bench that he was unable to continue, before he made his way to the sidelines with his body language suggesting he was close to vomiting. He was then helped by two Tottenham officials to the dressing room, with Moussa Sissoko sent on in his stead.

Concussion awareness is currently a hot topic in various sports across the world, as modern medicine has begun to more accurately detail the ravages that a professional sports career can have on brain health. As such, many football fans have taken to social media to voice their opinion on how Tottenham came to the decision to allow the clearly dazed player to return to action.

Jan Vertonghen is not in a good way after crashing into Toby Alderweireld.#UCL#TOTAJX#OptusSportpic.twitter.com/wCP45sHH29 — Optus Sport (@OptusSport) April 30, 2019

Time to bring in head injury assessments in football. Vertonghen should not have been allowed back on the pitch — Sponge Sports (@monkey_sponge) April 30, 2019

Right or wrong (and it's clearly wrong here), concussion assessments won't be done properly in football until the player can be temporarily replaced. Too much temptation to rush it while 10 men are being overrun. Easy fix. Do it. — Michael McCarthy (@McCarthyMick) April 30, 2019

How was Vertonghen allowed back on!? — Gavin Cooney (@gcooney93) April 30, 2019

Vertonghen being allowed to carry on with a head injury that caused bleeding was the equivalent of a battered boxer not being pulled out by his corner and suffering more punishment. Ridiculous. #TOTAJA — Danny Armstrong (@DannyWArmstrong) April 30, 2019

Vertonghen looks like he's going to vomit. — Miguel Delaney (@MiguelDelaney) April 30, 2019

Nothing worse than a filthy concussion. Poor Vertonghen 🤢 #TOTAJA — Niall McGrath (@niallmcgrath4) April 30, 2019

That was quite scary with Vertonghen. — Dermot Corrigan (@dermotmcorrigan) April 30, 2019

Good on Vertonghen for taking himself out of the game, but it's shameful on behalf of the Spurs coaching staff and doctors as well as the referees for allowing him to temporarily carry on. Maybe this can be a turning point for head injuries in football. — Jack Grimse (@JackGrimse) April 30, 2019