Former Tottenham defender Jan Vertonghen has revealed he played through concussion symptoms for nine months as he fought to earn a fresh contract.
Vertonghen was injured in Spurs' Champions League semi-final first leg against Ajax in 2019 at the Tottenham Hotspur Stadium after clashing heads with team-mate Toby Alderweireld.
The defender was allowed back into the game after prolonged checks by the Spurs medical team on the sideline, but as he realised his symptoms were too severe to continue, Vertonghen quickly signalled to the bench to be taken off.
Vertonghen, who left Spurs at the end of last season to join Benfica after failing to agree a new deal, told Belgian outlet Sporza the effects of the injury led to him losing his place in the team.
"Many people don't know this, but [the head injury against Ajax] affected me for a really long time. I had dizziness and headaches," he said. "The other day, there was the story about David Luiz and [Raul] Jimenez, in which Jimenez suffered a fractured skull.
"With me, it was my nose and I continued to play, which I shouldn't have done, according to the doctors. In the end, I think I suffered from that head injury for about eight or nine months. That was the reason why I didn't play well.
"I had a year left on my contract and I thought I had to play because I had to showcase myself to other clubs and to Tottenham, but when I played, I was rubbish. I just couldn't produce a good performance. Not many people knew that.
"That was my own choice and not a criticism of anyone else. After five months, there was a day when I started to feel better. When I see the footage from that time, I know when I didn't feel well by looking at myself.
"I think it was in January that I really didn't know what to do. Match after match, training session after training session, there was more impact. Then it was lockdown, so I didn't do anything for two months and after that it was better."
Tottenham released a statement on Vertonghen two days after he suffered the injury, in which they said that all FA concussion guidelines were followed.
It read: "Following a thorough review over the past 48 hours by our medical staff as well as by an independent neurologist with special interest in sport-related concussion today (Thursday, May 2, 2019), it has been concluded that Jan Vertonghen did not suffer a concussion during Tuesday's Champions League semi-final first leg against Ajax.
"The Belgium defender suffered an injury to his nose due to a challenge during the game which resulted in heavy bleeding. He was deemed fit to continue playing after an on-field assessment. All Football Association concussion guidelines were followed.
"Jan was immediately withdrawn as a result of the player informing medical staff that symptoms were developing suddenly and that he no longer felt stable standing up. We have been advised that this was the result of a presyncopal episode, a near faint.
"The specialist has recommended that the player undertakes a brief period of rehabilitation before returning to training."
The Premier League is set to discuss the implementation of concussion substitutes this week, while a move from three substitutes to five for the 2020/21 season is also expected to be back on the agenda.
Representatives from all 20 clubs will attend a shareholders' meeting, where they will discuss the outcomes and findings from the International Football Association Board's (IFAB) gathering on Wednesday.
The technical panel of IFAB - which is responsible for the laws of the game - has proposed allowing clubs to temporarily replace a player who is suspected of sustaining a concussion.
If IFAB supports its technical panel's suggestion, then the Premier League clubs could be presented with proposals to implement concussion substitutes.