Moments from Novak Djokovic's tennis career (34 images)

Novak Djokovic of Serbia is the No. 1 ranked tennis player in the world. His ability to compete for a fourth straight title at the Australian Open, which starts Monday, is in jeopardy over a dispute related to his refusal to be vaccinated for COVID-19, running afoul of Australia's health requirements.

Novak Djokovic looks up and smiles after a long point while playing in the U.S. Open finals against Roger Federer in New York City on September 9, 2007. Photo by John Angelillo/UPI

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Fans of Djokovic hold signs supporting him during his final match against Guillermo Canas at the Sony Ericsson Open in Key Biscayne, Fla. on April 1, 2007. Photo by Susan Knowles/UPI

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Djokovic returns the ball during his quarter-finals match against Russian Igor Andreev at the French Open in Roland Garros near Paris on June 6, 2007. Photo by Eco Clement/UPI

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Djokovic shows off his Rogers trophy for winning his final match against Federer in the Rogers Cup ATP Masters Series at Uniprix Stadium in Montreal on August 12, 2007. Photo by Grace Chiu/UPI

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