Premier League players are reportedly concerned that recent on-field heart problems are a possible consequence of taking the Covid-19 vaccine.
There have been a number of recent high-profile incidents involving players enduring heart problems on the field - including Christian Eriksen who collapsed due to a cardiac arrest at the European Championships and Sergio Aguero who was forced into retirement after he was diagnosed with heart arrhythmia.
The worrying spate of heart-related episodes in football has raised concerns over links with Covid and the vaccination programme to prevent it.
As reported by the New York Times, recent incidents have 'fueled suspicion' of the vaccine among some players that there is a connection.
Medical staff at certain clubs are said to believe the suspicion has been 'encouraged' by a handful of retired players, including Matthew Le Tisser and Trevor Sinclair, who have questioned whether issues have been a possible consequence of taking the vaccination.
Speaking to GB News, as per the Express, Southampton legend Le Tissier called for an investigation on whether the vaccine has contributed to the rising number of footballers suffering from heart problems.
He said: 'It's been very concerning to me that in all that time I never once saw any footballer leave the pitch because of heart issues.
'Now I'm sorry but if anybody can look at what is happening now in the world of sport and say it's normal for all of these people to be having heart issues in football matches, cricket matches, basketball matches, any sport you wish.
'The amount of people that are suffering is going through the roof. And I would call for an investigation because it might not be to do with the vaccine.'
Former West Ham and England player Sinclair meanwhile tweeted last month: 'Everyone I speak to about these heart problems suffered by footballers (which worryingly seem to be happening more regularly) are they linked to covid vaccines or not??'
Inter Milan director Giuseppe Marotta though said that their now former player Eriksen had not taken a Covid vaccine before his collapse for Denmark against Finland at the Euros.
Earlier this week, the Premier League confirmed that 84 per cent of players are 'on the vaccination journey' - meaning they have had at least one dose of the vaccine.
77 per cent of Premier League players have received two doses of Covid vaccines and are classed as fully vaccinated.
That figure indicates that 16 per cent of stars - around 100 players - are still yet to receive their first dosage.
In total, 92 per cent of players and staff have received one, two or three doses, yet these figures pale in comparison to those shared by top leagues across Europe. Germany's Bundesliga have revealed that 94 per cent of players and staff are vaccinated, while Italy's Serie A's vaccination rate is 98 per cent.
There have been a number of other worrying incidents across Europe involving players this season.
Manchester United defender Victor Lindelof wore a heart monitor for two days after he went off against Norwich clutching his chest.
There were similar incidents this month involving Napoli midfielder Piotr Zielinski and Martin Terrier of Rennes, while Partizan Belgrade player Ricardo Gomes collapsed in training.
In November, Wigan manager Leam Richardson had to give CPR to striker Charlie Wyke after he went into cardiac arrest in training and just days later Sheffield United's John Fleck was carried off in a game at Reading.
Adama Traore of Sheriff Tiraspol was at the centre of another scare during a Champions League tie against Real Madrid and Emil Palsson technically died for four minutes during a Norwegian Second Division game between Sogndal and Stjordals-Blink amid scenes reminiscent of Eriksen's collapse.
There have also been Premier League games which have been briefly stopped due to heart issues for fans in the grandstands.
A Watford fan suffered a cardiac arrest and required CPR in their clash with Chelsea, while doctors also helped save the life of a Newcastle fan who collapsed in their match against Tottenham.
Professional Footballers' Association (PFA) chief executive Maheta Molango backed the 16 per cent of unjabbed footballers by pointing out that they had to play without Covid vaccines last year.
'We have to be careful with over-simplistic assessments of situations,' Molango told the BBC.
'(The players are) the same people that a few months ago, when I was at home and most people were at home, were told go out and play with no vaccines, that there were "no worries, you're going to be fine".'
Molango said some players may have 'legitimate concerns' in deciding not to take a coronavirus jab but the PFA is trying to help them make the 'right choice'.
We're trying to help the players make the right choice based on science,' he added.
'They need to listen to the experts but at the same time, we have to acknowledge that certain people may have legitimate concerns.'