Robin Soderling joins Roger Federer on the sidelines for the mandatory Shanghai Masters 1000 tournament, which begins October 9. Federer says he is tired after a long summer and Soderling is not over his case of mono. Novak Djokovic is also questionable for that event as well as the China Open in Beijing.  The No. 1 suffered a back injury at the US Open which grew worse at Davis Cup, where he had to retire in his match against Juan martin Del Potro. He said  he may have to skip his next tournaments in China and thta his recovery could take a month. "I hope I will recover by then," Djokovic said. "Anyway, I won't risk the worsening of the injury and that's why it is hard to predict for how long I will rest."