Novak Djokovic apologized and said his injury 'hurt' after tennis fans mercilessly booed him off the US Open court

• Novak Djokovic was booed off court after retiring from his US Open third round match against Stan Wawrinka.
• The Serb called time on his tournament early in the third set after losing the opening two 6-4, 7-5.
• "It is very frustrating. Of course it hurts that I had to retire," said Djokovic in The Guardian.
• On the booing crowd, the Serb said: "You cannot blame them."
• Djokovic's exit means he has failed to retain his US Open title, with Rafael Nadal and Roger Federer now the favorites to win the tournament.
• Visit Business Insider's homepage for more stories.

Novak Djokovic was booed off court after retiring from his US Open third round match against Stan Wawrinka.

The Serbian, who has won the tournament three times previously, withdrew from the match with a shoulder problem in the third set, having lost the opening two.

"I'm sorry for the crowd. They came to see a full match but it wasn't to be," said the world number one in The Guardian. "I mean, a lot of people didn't know what's happening, so you cannot blame them."

Listen to Djokovic get booed here:

Djokovic was dominated by Wawrinka in front of a capacity crowd at the Arthur Ashe Stadium at Flushing Meadows in Queens, with the Swiss storming to take a 6-4, 7-5, 2-0 lead, at which point Djokovic decided he could not continue.

Last year's US Open winner had shown signs of his injury in the second round against Juan Ignacio Londero, where he needed treatment three times before eventually overcoming the Argentine in straight sets.

The problem seemed to have mostly subsided in his third round victory over American Denis Kudla, however it returned to haunt him against Warwinka, who will now face Daniil Medvedev in the quarterfinals on Tuesday.

"It is very frustrating. Of course it hurts that I had to retire," said Djokovic in The Guardian. "Some days the pain has been higher, some days with less intensity. Obviously I was taking different stuff to kill the pain instantly. Sometimes it works, sometimes it doesn't."

Read more: An American tennis player has been fined $10,000 for pointing his tennis racket like a rifle at a US Open official

Djokovic's exit paves the way for Rafael Nadal or Roger Federer to extend their advantages over the Serb in the race to be the most decorated men's tennis player of all time.

Djokovic has won 16 grand slam titles, while Nadal was won 18 and Federer 20.

Nadal faces Marin Cilic in the round of 16 on Monday, and Federer takes on Grigor Dimitrov in the quarterfinals on Tuesday.