Scientists have countered claims linking the Covid-19 vaccine with an increase in the number of footballers developing heart problems.

On-field emergencies involving Wigan’s Charlie Wyke, John Fleck, of Sheffield United, and Sheriff Tiraspol’s Adama Traore prompted wild speculation.

However, experts have pointed to research showing that previous coronavirus infection would be a more likely contributory factor than the jab, if there was any link at all.

A recent American study found that younger people infected with the virus were up to six times more likely to develop myocarditis than those who received the vaccine.

“Anything the vaccines do, natural infection will almost certainly be more common with disease,” said Prof Keith Neal, who has 25 years of experience in the research of the epidemiology of infectious diseases at the University of Nottingham.

Prof Jonathan Ball, a molecular virologist at the same university, added: “Studies have shown that Covid is more likely to cause myocarditis and pericarditis than the vaccines.”

The pair, who referenced research by universities and heart centres in Ohio, had already expressed their concern about former players sparking fears the vaccine had contributed to the recent health alerts.

Prof Neal said there was no evidence to show conclusively that any aspect of Covid was impacting on health in elite sport. “But these things are always investigated if reported,” he added.

Wyke, Fleck and Traore were still undergoing tests on Friday as administrators in other sports faced up to the prospect of more restrictions due to a virulent new strain.

Rugby, cricket and golf fixtures have already been disrupted in South Africa, and there will be inevitable nervousness that the Africa Cup of Nations in Cameroon may be plunged into chaos from January 9.

On Friday, Welsh rugby union clubs Cardiff and Scarlets were making efforts to fly home immediately from the United Rugby Championship after the Government put South Africa on its red list.

“With the situation in South Africa having changed so quickly, we are now looking to repatriate our staff ASAP,” Cardiff said on Twitter.

Munster and Zebre were also due to play in South Africa. “The United Rugby Championship is working with the four visiting clubs … to facilitate their return as soon as possible,” a URC statement said.

They were the first clubs to arrive in South Africa since the onset of the pandemic and the postponement of fixtures will come as a major blow to the newly-launched tournament, involving sides from South Africa, Ireland, Italy, Scotland and Wales.

Golf’s Joburg Open, the first European Tour event of the new season, was also hit by withdrawals. A total of 19 golfers from Britain, Ireland, Denmark and Germany either withdrew before play or retired during their Friday rounds.

In cricket, South Africa began the first of a three-match one-day international series against Holland, but the second and third games appear certain to be called off.

With the world facing a fresh wave of infections, scientists said it was unwise of sporting pundits to continue questioning the wisdom of having the jab.

TalkSport was forced to cut off Trevor Sinclair from a broadcast this week as he questioned whether Fleck, who collapsed against Reading on Tuesday, had recently had the jab. “I think everyone wants to know if he [Fleck] has had the Covid vaccine,” he said.

Former professionals, such as Ramon Vega and Matthew Le Tissier, had demanded investigations, prompting scientists to remind them of their “public responsibility”. “Given the track record of certain footballers in the field of anti-vaccine beliefs, it is totally irresponsible to make unsubstantiated comments, as opposed to getting them properly dealt with,” Prof Neal had said.

Prof Robert Dingwall, a public health specialist at Nottingham Trent University, said: “There are many reasons why on-field collapses may occur, even in clusters. We should all be careful not to blame any particular cause until they have been properly investigated. It may be tempting to blame Covid vaccines but pundits do have a public responsibility not to fuel vaccine hesitancy without any real evidence that this is a common factor in widely separated events.”

Prof Dingwall later added: “There have long been suggestions that elite athletes should take particular care in returning to full training or performance after any viral infection. It would not be surprising, then, if even a mild Covid infection were to have a greater impact on this group than on the general population. However, there is a lack of evidence to establish that a specific virus caused a particular event or set of events.” 

Misinformation was spread after Denmark’s Christian Eriksen suffered on-field cardiac arrest during Euro 2020 in the summer. Inter Milan have since confirmed that he had not even had his first jab at the time of his collapse.