The White House on Wednesday stood by a vaccine mandate for foreign visitors that could keep tennis star Novak Djokovic from playing in the Miami Open.

Gov. Ron DeSantis (R-FL) penned a letter to President Joe Biden earlier this week asking for an exemption so Djokovic could play in the Miami Open. But it doesn't appear that is going to happen.

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"I would refer you to the CDC, they are the ones who deal with that," White House press secretary Karine Jean-Pierre said in response to a reporter's question. "It's still in place, and we expect everyone to abide by our country's rule, whether as a participant or a spectator."

DeSantis, a potential 2024 presidential candidate, called the mandate "unscientific."

"The only thing keeping Mr. Djokovic from participating in this tournament is your administration's continued enforcement of a misguided, unscientific, and out-of-date COVID-19 vaccination requirement for foreign guests seeking to visit our great country," DeSantis wrote in a letter obtained by the Washington Examiner.

DeSantis also requested that the Biden administration confirm by March 10 that Djokovic cannot enter Florida by boat. He noted in a footnote that Biden's Oct. 25, 2021 proclamation "governs the entry into the United States of noncitizen nonimmigrants ... by air. "

"Your administration does not appear to have issued analogous restrictions for non-U.S. individuals seeking to enter our country by boat," he added in the footnote.

Earlier this year, Djokovic won the Australian Open for the 10th time after having been blocked from last year's tournament for his refusal to take the COVID-19 vaccination. He recently withdrew from the Indian Wells tournament.

Djokovic has run into hurdles in gaining entrance to the U.S. to play the Miami Open, which runs from March 19 to April 2, due to his lack of vaccination. An outcry of Republicans and conservatives such as Sens. Marco Rubio (R-FL) and Rick Scott (R-FL) has urged the Biden administration to ease up and allow him into the U.S., though Jean-Pierre's response puts those calls in doubt.

Notably, though DeSantis was mentioned in the question, Jean-Pierre did speak about him directly in her answer, in a break with past practice.

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Jean-Pierre also did not engage with whether or not the vaccine mandate was necessary, only saying that it's something the CDC recommends.

"This is something that the CDC speaks to," she said.