Two-time Australian Open champion Victoria Azarenka said she has pulled out of next week's Women's Tennis Association (WTA) 500 event in Stuttgart as it coincides with her scheduled COVID-19 vaccination.

"I will unfortunately not be able to compete in Stuttgart next week as I will be receiving my first dose of the vaccine at the same time," the Belarusian world No. 15 said via Twitter.

While both the Association of Tennis Professionals (ATP) and WTA Tours have encouraged athletes to accept vaccine shots when available, some top players expressed a reluctance to get vaccinated at the recent Miami Open.

Under updated COVID-19 protocols on the men's tour, players who have been vaccinated are no longer considered as close contacts of anyone testing positive for the coronavirus.

The pandemic has forced sporting events, for example, tennis tournaments to be held behind closed doors or with a limited number of spectators.

The scenario of empty stands has been the new normal for tennis since last year.

In the tennis world, top players like Rafael Nadal and Novak Djokovic recently said they still find it difficult to maintain their intensity during matches without spectators.

Nadal lost some of his intensity during his 6-1, 6-2 win over Argentine Delbonis on Wednesday at the Monte Carlo Masters. The Spaniard believed it was the absence of fans that took something away from the game.

"It's difficult to keep going sometimes with the same intensity without the crowd," the 20-time Grand Slam champion said. "The crowd helps you to keep going. You want to show that you are in good shape."

"It's true, personally I miss the crowd. I can't lie about that. I enjoy much more playing in front of a good crowd than without," he added.

Also, on Wednesday, men's tennis world No.1 Djokovic produced a high-level performance to beat Italian 19-year-old Jannik Sinner 6-4, 6-2 at the ATP Masters 1000 event.

And he also said he missed the energy generated by spectators. "We need crowds back on the stands. The crowd gives us so much energy. Also, it adds to the motivation in a sense to what we do, the sport that we are a part of."

"We have this calm and kind of serenity in the stands and on the court," he added. "It just allows you to maybe focus on yourself a bit more."

(With input from Reuters)