Novak Djokovic was waiting on Saturday to learn whether he would get last-minute clearance to enter the United States to play at Indian Wells and Miami, as American tennis chiefs threw support behind the world number one.

US senator Rick Scott claimed Djokovic has been refused permission by the US Department of Homeland Security for a vaccine waiver and urged president Joe Biden to intervene on behalf of the Serbian and "fix this NOW".

Scott was backed by fellow senator Marco Rubio, who wrote on Twitter: "@DjokerNole [Djokovic] shouldn’t be prohibited from playing in the @MiamiOpen because of unconstitutional vaccine mandates.

"@POTUS [Biden] should immediately grant Djokovic a waiver to the vaccine mandate for international travellers."

Djokovic has refused to be vaccinated against COVID-19 and that stance has cost him places in two grand slam tournaments, being deported before last year's Australian Open and then denied permission to compete at the US Open later in the season.

It has also meant he has had to miss regular tour events in the United States, which demands international travellers are fully vaccinated.

Scott and Rubio are both senators for Florida, and accordingly their focus is on the Miami Open, which runs from March 22 to April 2.

More pressingly for the 35-year-old Djokovic, the Indian Wells tournament begins in the coming week, with main draw singles matches getting under way on Wednesday.

A statement posted on the US Open Twitter page confirmed support for the 22-time grand slam winner.

It read: "Novak Djokovic is one [of] the greatest champions our sport has ever seen.

"The USTA and US Open are hopeful that Novak is successful in his petition to enter the country, and that the fans will be able to see him back in action at Indian Wells and Miami."