Djokovic, a former world number one, retired hurt during the quarter-finals at Wimbledon and said he was considering taking a break from playing to recover from the long-standing injury to his right elbow.
Serbia’s Sportski Zurnal reported that the 30-year-old could face up to 12 weeks on the sidelines.
“He has a bruised bone due to excessive playing,” it quoted Zdenko Milinkovic as saying.
“Novak is in Toronto undergoing some further tests with specialists.”
The 12-times grand slam champion won the U.S. Open in 2011 and 2015. This year’s tournament, which begins on Aug. 28 will offer a record $50.4 million in prizes, according to the organizers, United States Tennis Association, USTA.
Winners of the men’s and women’s singles titles will each earn $3.7 million, while runners-up will pocket $1.825 million from the $50.4 million total pot.
The men’s and women’s doubles champion teams will each earn $675,000, also the highest in U.S. Open history.
The qualifying tournament for the season’s final grand slam will offer more than $2.9 million in prize money, a 49.2 percent increase from 2016.
“Five years ago, we committed to the players that total player compensation for players would reach $50 million at the U.S. Open, and we are honouring that commitment,” USTA President Katrina Adams said in a statement.