Novak Djokovic could reportedly be banned from taking part in at least three of the four Grand Slam tournaments this year.
The world number one lost a bitter public battle to take part in the Australian Open this month due to the country's strict coronavirus restrictions.
Djokovic saw his visa revoked and failed with an appeal against the decision before being deported back to Serbia, unable to defend the title he has won in each of the last three years.
The 20-time Grand Slam champion could be set for further disappointment later in the year too, with current rules in France and New York preventing unvaccinated players from featuring.
France will soon bring in a mandatory COVID pass for over-16s, and the French government have now ruled that all athletes will have to be vaccinated in order to attend and compete in sporting events in the country.
New York rules also prohibit unvaccinated athletes from competing in sporting events in the state.
As things stand, Wimbledon is the only Grand Slam Djokovic will be eligible to take part in this year should he remain unvaccinated, although the organisers at the All England club are understood to have offered no guarantees on that front either.
Djokovic won three of the four Grand Slam titles last year, only being denied a calendar slam when he lost the US Open final.