Undated, Jul 25 (Reuters) Former world number one Novak Djokovic is in doubt for the US Open due to his elbow injury, Serbian media reported, citing the country's Davis Cup team doctor. Djokovic 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 US Open in 2011 and 2015. This year's tournament begins on August 28. REUTERS JW