Tottenham defender Jan Vertonghen had to be helped off the field shortly after trying to continue to play following a clash of heads in their 1-0 Champions League semifinal loss to Ajax on Tuesday.

Vertonghen challenged for a header in the Ajax area just after the 30-minute mark, but slammed his face into the back of teammate Toby Alderweireld's head, leaving him with blood pouring from a cut on his nose. Vertonghen received treatment on the field and went to change his bloodied white jersey before returning to the game.

Referee Antonio Mateu Lahoz was pointing at his head as he spoke to Vertonghen, before allowing him to return to action in the 38th minute.

He didn't last long before going across to the sideline, leaning over and struggling to stand. He had to be helped down the tunnel by two medical officials and was replaced by Moussa Sissoko.

UK broadcaster BT Sport said that Vertonghen remained in the stadium dressing room after the incident and was being looked at by medical staff.

Following the match, Tottenham manager Mauricio Pochettino said of Vertonghen: "I don't know; I didn't see him. Of course, we will assess in the next few days and will see."

Multiple reports following the match said that Vertonghen passed concussion tests and was also seen walking through the mixed zone after leaving the dressing room.

When asked about allowing Vertonghen to return to the field, Pochettino said it was a decision made by the team's medical staff.

"I wasn't involved, that was a doctor decision," Pochettino said. "I think it's so important things that the rules and the protocol are there and the medical staff follow the protocol. I was never involved, the decision was the doctors and the referee then asked to put him in and said 'go in' and in this action we need to put him out because he didn't feel well.

"Tt wasn't my decision, I repeat. For me, first of all its your life. We must protect the player and of course I was out of the conversation and our medical followed the protocol and decided it was possible to restart the game and it's time to play again.

"But of course it was Jan in that moment and the following action that he started to follow unwell and we check him with the doctor."

Pochettino said he hoped that Vertonghen wouldn't have any more issues following the knock and said he appeared to look OK when he left the stadium.

"He was walking away from the stadium now," Pochettino said. "I hope he is well and you know very well that always you need to keep eyes watching him, others beside him because it was a big knock. I hope it is not a big issue but at the moment he is OK."