Sources said Jinping, who is expected to be announced as the new leader of the Communist Party in the coming weeks, has suffered a mild heart attack.
"Although people have said he suffered a back injury, he actually had a heart attack, a myocardial infarction," said Li Weidong, a political commentator in Beijing and the former editor of China Reform.
According to the Telegraph, other unnamed sources have also suggested that Xi, 59, suffered a heart attack, while Willy Lam, former editor of the South China Morning Post, believes China's president-in-waiting had a stroke and is currently unable to show his face in public.
Xi has not been spotted since September 1. He even cancelled a series of meetings with foreign leaders, including one with United States Secretary of State Hillary Clinton on September 4.
The Communist Party has remained tight-lipped about him. For the third day in a row, the foreign ministry has not responded to repeated questions about Jinping's absence. A spokesman merely said, "I have no information".
According to the report, rumours suggest that Xi, in fact, was perfectly healthy, but had important work.
A magazine in Hong Kong, iSun Affairs, said Xi's relative had sent a text message indicating that 'all is well'.
At Beijing's Military Hospital, the facility that often treats top leaders, there was no sign of any extra security. Staffers said they had not noticed any unusual activity and that they did not know if Xi was in the compound.
Linda Jacobson, a China expert at the Lowy Institute for International Policy in Sydney, wrote in a comment piece that if Xi was genuinely ill, she would expect senior leaders to change their schedules.
"That is standard Communist Party practice at a time of crisis," she noted, adding, "Yet Hu Jintao did not cut short his trip to Vladivostok for the Asia Pacific Economic Cooperation Forum. Another senior leader, Wu Bangguo, travelled to Iran. A third high-ranking official visited Sichuan this week."