Hobbled Wawrinka pulls out of U.S. Open

NEW YORK — Defending champion Stan Wawrinka pulled out of the U.S. Open because of an injured knee. He will have a medical procedure and sit out the rest of 2017.

“This was the only solution to make sure I will be able to compete at the top level for many more years,” Wawrinka said Friday in a statement through his agency.

He joins the man he beat in last year’s final at Flushing Meadows, Novak Djokovic, in calling it quits for this season because of injury.

The fourth-ranked Wawrinka added last year’s title to his 2014 Australian Open and 2015 French Open championships. The 32-year old Swiss got back to the finals in Paris in June, losing to Rafael Nadal, but was eliminated by Daniil Medvedev in the first round at Wimbledon. In other tennis news: • Top women’s seed Simona Halep retired from her quarterfinal match at the Citi Open because of the heat, allowing Russia’s Ekaterina Makarova to advance to the semifinals in Washington. Fourth-seeded German Julia Goerges beat Monica Niculescu 6-3, 6-4, to advance.

• Philipp Kohlschreiber and Joao Sousa advanced to the final of the Generali Open in Kitzbuehel, Austria, with both players seeking their first title of the season. Sousa ended the run of Austrian wild card Sebastian Ofner with a 7-6 (4), 7-6 (4) win. Earlier, Kohlschreiber beat second-seeded Fabio Fognini 7-5, 6-3.