Professional sports are just one sector of society that has struggled to carry on despite the worst global pandemic in a century. Play quickly ground to a halt almost everywhere in Europe and North America when COVID-19 broke out there in March. But weeks and months later, many leagues and other competitions gradually returned to action – often in modified formats. 

The Bundesliga led the way in European football, restarting with Geisterspiele  or "ghost games" played behind closed doors in May, managing to complete the 2019-20 season by the end of June. Thanks to the hygiene plan drawn up by the DFL (German Football League), the Bundesliga has seen relatively few infections, but there have been some, particularly when players have returned from international duty.

Perhaps the highest-profile case in Germany has been that of Hoffenheim striker Andrej Kramaric. The 29-year-old had been the Bundesliga's top scorer with six goals in the first three games of the season prior to the international break in October. The Croatia player was just one of a number to test positive for COVID-19 after returning to his club, and the coronavirus would keep him out of action for more than a month. When he did return, on Matchday 8, he appeared no worse for wear, adding to his goal total from a spot kick.

Elsewhere, Liverpool duo Mo Salah (pictured, top) and Sadio Mane are have both missed matches after contracting the virus, while matches in the Premier League, the NFL and several other sports in a number of countries have been postponed after outbreaks.

Risk of complications

However, despite a widely held perception that the coronavirus is only really dangerous for the elderly or people with preexisting health conditions, the case of a player in Germany's top ice hockey league, the DEL, has demonstrated that contracting the virus can have serious consequences beyond COVID-19 – that the athlete may not even notice. 

In October, Janik Möser, a defenseman with the DEL's Wolfsburg Grizzlys, tested positive for the coronavirus. After 10 days of self-quarantine Möser thought he was good to go and was keen to hit the ice again to prepare for the DEL season, the start of which has been delayed by a couple of months. 

"The course (of the infection) was relatively mild," Möser told reporters at a recent press conference organized by the league. "I had mild symptoms and never felt extremely ill."

Fortunately for him, though, as a precaution, the Grizzlys' medical team insisted on conducting a series of tests before allowing him to return to the ice. The tests found that Möser, who said he felt perfectly fit at the time, had developed a serious health issue – that the doctors believe was brought on by his COVID-19 infection. 

Nothing more strenuous than a leisurely stroll

"At the Charité (hospital) in Berlin, an examination revealed an inflammation of the heart muscle," the Grisslys' team doctor, Axel Gänsslen, told reporters. "This can be a trigger for sudden cardiac death."

As the doctor went on to explain, the real danger comes when the patient achieves a high heart rate associated with physical exertion. This is why the 25-year-old is under strict instructions from Wolfsburg's medical staff to avoid doing anything more strenuous than a leisurely stroll – and to regularly monitor his heart rate. 

An inflammation of the heart muscle can take months to heal – even for an elite athlete, so Möser won't be allowed to return to the ice until at least January – and that will be conditional upon him being cleared to do so in a fresh battery of medical tests.  

Coronvirus 'often attacks cardiovascular system'

Möser's case didn't come as a particular surprise to Professor Hans-Georg Predel of the German Sport University in Cologne. He and his staff have been studying the longer-term effects that a coronavirus infection can have on the health and performance of athletes. 

"It is almost misleading to describe COVID-19 as a 'new type of lung disease'," Professor Predel told DW. "Very often the virus also attacks the cardiovascular system." 

For this reason, he recommends that athletes be examined "routinely and carefully" for any damage or irregularities.

"COVID-19 can also lead to considerable changes in the heart area in young adults," the Grizzlys' Dr. Gänsslen confirmed. 

For his part, Möser said he hoped that his case would serve as a vital warning for others.  

"I wanted to go public with my case," he said. "It should not be taken lightly, and it can also affect young healthy people like me."