Former Tottenham defender Jan Vertonghen says he felt the effects of a concussion he sustained playing for Spurs for the following nine months.
The 33-year-old Belgium international collided with Spurs team-mate Toby Alderweireld and Ajax goalkeeper Andre Onana during the teams' Champions League semi-final in April 2019.
He tried to play on before he was led off and appeared to vomit.
"I suffered a lot from that - dizziness and headaches," said Vertonghen.
"I should not have continued playing, it affected me in total for nine months and that's why I couldn't bring what I wanted to on the field."
Vertonghen, who moved to Benfica in August this year, told Belgian broadcaster Sporza that the injury contributed to a dip in his form during his final season at Tottenham.
"I still had a year left on my contract, so I had to play, but when I played, I played badly," added Vertonghen.
"The fact I got benched had nothing to do with him [manager Jose Mourinho]. I was in a period [when] I could not bring what I should have. I even thought he played me a lot, compared to how I performed."
The International Football Association Board (Ifab) is due to discuss the possible introduction of temporary concussion substitutes to allow a more accurate diagnosis of head injuries.
The issue has been in the spotlight after several members of England's 1966 World Cup-winning team were diagnosed with dementia.
Nobby Stiles and Jack Charlton, who both died earlier this year, had dementia, while Sir Bobby Charlton's family recently revealed he had been diagnosed with the disease.
"We are looking at the number of players who are getting dementia and trying to establish a causal link," Professional Footballers Association chief executive Gordon Taylor told Sky Sports News.
"I don't know any footballer who regrets his career, but we also have a duty of care and I think it is incumbent on the authorities that we don't put off any youngster coming into the game because of worries about the future."
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