Nadal published a statement on social media in which he said it had "been a hard year - very good on a tennis level when I have been able to play and, at the same time, very bad as far as injuries are concerned".
Five-time champion Djokovic was drawn in Group Guga Kuerten on the day he returned to the top of the rankings and Rafael Nadal withdrew from the season-ending tournament due to ankle and abdominal injuries.
Cape Town - It's a case intriguingly of what he can achieve, what he can't achieve and what he will achieve when top South African tennis player Kevin Anderson competes in his first ATP Finals next week.
The Spaniard has been struggling with an abdominal injury and was forced to pull out of the Paris Masters last week. Also, the World Number one surrendered to the Australia Open finalist, Cilic at the Queen's final.
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The caravan, estimated at about 3,500 people, is now hundreds of miles away and would take at least six weeks to reach the border. These include putting up more fences, creating temporary vehicle barriers and operating heavy machinery.
Djokovic, 31, underwent elbow surgery in January and slipped to 22nd in the world after a depressing quarter-final exit at Roland Garros in June, which left him briefly threatening to skip Wimbledon.
The beaten finalist at Melbourne Park in 2017, Nadal saw his Australian Open campaign end in painful fashion this January.
The issue was serious enough to also rule Nadal out of the Masters 1000 events in Indian Wells and Miami, but he went on to enjoy familiar success on clay, including yet another French Open title.
After leading Serbia to a maiden Davis Cup in 2010, he raced through the first half of 2011, building up a 48-1 winning run.
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The movie has a tentative title of " Greenbrier ", and will follow " the escape of a kidnapped man and his quest for freedom ". The Journal also reports that the project now has the working title Greenbriar - though that could just be a holding name.
Despite his successes, Nadal's season was marred by health woes.
A few weeks later he beat Del Potro in the final to win the US Open and last month claimed the Shanghai Masters title without dropping a set.
Off court, Djokovic married long-time girlfriend Jelena Ristic in July 2014.
However, despite his achievements, Djokovic appears doomed never to be held in the same warm esteem as Federer and Nadal.
Alexandria Ocasio-Cortez wins election to New York’s 14th congressional district
Democrats Sharice Davids of Kansas and Debra Haaland of New Mexico became the first Native American women elected to Congress. Democrat Janet Mills of ME and Republican Kristi Noem of South Dakota are the first women elected as governor in their state.