The Australian Open will require players to be fully vaccinated.

The Australian Open in January will become the first Grand Slam tennis tournament to require that players be fully vaccinated against the coronavirus, a decision that casts doubt on the participation of Novak Djokovic of Serbia, the No. 1-ranked men’s player, who has declined to divulge his vaccination status.

Craig Tiley, the Australian Open tournament director, confirmed the tournament’s policy in a television interview in Melbourne on Saturday.

The announcement ended months of speculation and mixed messages from Australian government officials. Federal authorities had indicated that unvaccinated players might be able to enter Australia and compete in the tournament in Melbourne after a 14-day quarantine period. But Daniel Andrews, the premier of the state of Victoria, has been adamant that players will need to be fully vaccinated, just as Australian Open spectators and on-site employees will be required to be vaccinated.

Melbourne, Victoria’s capital, has experienced some of the strictest coronavirus measures in the world, with six separate stay-at-home orders over an 18-month period.

“It is the one direction that you can take that you can ensure everyone’s safety, and all the playing group understands it,” Mr. Tiley said of requiring players to be vaccinated. “Our patrons will need to be vaccinated. All the staff working the Australian Open will need to be vaccinated, but when we’re in a state where there’s more than 90 percent of the population fully vaccinated — they’ve done a magnificent job with that — it’s the right thing to do.”

Steve Simon, the chief executive of the Women’s Tennis Association, said in an interview this past week that “over 70 percent” of the W.T.A.’s top 300 singles players and top 100 doubles players had been vaccinated and that all of the singles and doubles players who competed in the recent W.T.A. finals in Mexico had been vaccinated.

Andrea Gaudenzi, the chairman of the men’s tour, said in an interview on Friday that the vaccination rate for the top 100 men’s singles players was “above 80 percent.”

“We are moving toward 90 percent, 95 percent of fully vaccinated,” he said. “A lot will do it in the off-season with one shot.”

But it seems all but certain that some qualified players will not make the journey to Australia because of the policy.

All four Grand Slam tournaments, including the U.S. Open, allowed unvaccinated players to participate this year, as have regular tour events.

Djokovic, a nine-time Australian Open singles champion, has yet to confirm whether he will defend his title next year. He and his wife, Jelena, contracted the coronavirus in June 2020 during an exhibition tour that he had helped to organize in Serbia and Croatia.

He has expressed concern about vaccines and has said repeatedly that he would wait for the Australian Open’s policy to be made clear before making a decision on participating.