Jan Vertonghen suffers head injury but is allowed to play on before being helped off

The Tottenham defender collided with Ajax keeper Onana and team-mate Toby Alderweireld midway through the first period of the Champions League semi-final as he went up for an aerial ball in the box.

The Belgian lay prone on the ground before he was treated on the pitch for two minutes to stem the blood pouring from a cut on his nose.

Despite visibly being in discomfort, Vertonghen returned to the field of play following further medical attention pitchside.

Such was the ferocity of Onana's challenge, Alderweireld was also caught in the back as he came to punch the ball clear.

After Vertonghen had come back on the pitch, with a new shirt to replace the blood-stained original, the 32-year-old signalled immediately to the sidelines that he needed to be replaced.

There were concerning scenes as Vertonghen had to be assisted off the pitch by two physios, clearly suffering from concussion.

The experienced centre-back appeared to vomit with his right leg going limp as Moussa Sissoko showed concern for his team-mate before replacing him.

Mauricio Pochettino put his arm around him as he made his way down the tunnel, but Tottenham will face strong criticism for opting to allow Vertonghen to return to the pitch, with former American international Taylor Twellman, who retired from the game due to concussion, leading the calls for stronger action to be taken.

"Vertonghen under NO CIRCUMSTANCES should have been allowed to come back onto the field.....DISGUSTING PATHETIC demonstration from @SpursOfficial medical staff!" tweeted Twellman, who has played an active role in promoting awareness of concussions since his retirement.

Twellman was not alone in voicing his opinion...