A study from Germany and Italy indicated that soccer players and other athletes are at risk of infecting their lungs with the emerging corona virus, which raises questions about attempts to resume the game's competitions.

The study - prepared by Italian immunologists and lung specialists at institutions in Berlin, Rome and Verona - says that older athletes are more likely to inhale the virus particles and direct them to the lower regions of the lung due to strenuous physical training.

Covid-19 can cause lung damage and complications, such as pneumonia and acute respiratory distress syndrome.

The study also - which still needs to be reviewed - indicates that athletes who did not show any symptoms may get worse by transferring infection to their lungs during heavy physical training.

All major leagues in Europe have stopped and none have resumed yet, and the European Football Association (UEFA) has set a deadline for the leagues that expires on May 25 in order to set plans to resume the competitions.

But the leagues, their responsible bodies and clubs have said they will only return when playing is safe and receive medical advice.

In the research paper, Paolo Matricardi, Roberto D. Negro and Roberto Nissini raised questions about safety of play, while the virus was still widespread.

The publishers of the study said that "specifically professional athletes are more likely (than ordinary individuals) to become infected with the virus because of their ongoing strenuous training."

The researchers say that the "ideal lungs" of athletes tend toward deep inhalation of infectious agents, even though they are a catalyst in normal circumstances.

The study added that the players who are infected with the virus and do not show any symptoms may get worse by allowing the virus to move down the airways.

Infected athletes may emerge and have no symptoms during the exhalation process, possibly carrying the virus and then inhaling it.

And yesterday, Tuesday, the International Athletic Federation - which represents about 85,000 athletes of different sports in more than 60 countries - said that professionals should not be in a hurry to return to competitions.

In turn, he urged the International Association of Professional Footballers to be cautious, too.