A blow to the head in the Champions League semi-finals last year left Jan Vertonghen dizzy and suffering from headaches for nine months, and ruined the last season of his contract at Tottenham Hotspur, the Belgium international said.

Centre back Vertonghen, who left Spurs for Benfica on a free transfer in August, was involved in a sickening collision with team mate Toby Alderweireld in the fixture against Ajax Amsterdam.

He had concussion symptoms for months, and was left fearing every coming together in training or a match.

"Lots of people don't know it but I suffered a lot from that hit: dizziness and headaches," he told Belgium’s Sporza TV on Tuesday.

"This is now the first time I tell about it. It affected me in total for nine months and that's why I couldn't bring on the field what I wanted to.

"I just didn't know what to do. It was game after game and training after training. Every time there was a new impact. Then the lockdown came and I was able to rest for two months, after that it was a lot better."

Vertonghen admits he felt compelled to keep on playing for the sake of his career, even though he knew it was affecting his performance.

"I had only one year of contract left, so I had to play. But when I played, I played badly. Not a lot of people knew about it, that was my own choice."

Vertonghen’s admission comes on the same day lawyers for a number of former rugby players sent a letter of claim to World Rugby, the Rugby Football Union and the Welsh Rugby Union in a class-action suit that alleges a failure to protect them adequately has led to early onset of dementia.

The combined claims are expected to amount to millions of pounds in damages.