Zimbabwe opposition leader Morgan Tsvangirai is undergoing cancer treatment at a hospital in neighboring South Africa.
The 65-year-old leader of the Movement for Democratic Change has been in and out of the hospital since revealing last June that he had been diagnosed with colon cancer.
An unnamed party spokesman told reporters Tuesday that Tsvangirai has been hospitalized since January, and that he was in critical condition.
"We should brace for the worse," the spokesman said.
But Tsvangirai disputed the reports of his poor health in a post on his Twitter feed. "Of course I have cancer and not feeling too well but I am stable and the process is under control," he wrote.
He formed the MDC in 1999 to challenge President Robert Mugabe, who was forced out of office last November after a military uprising, ending his 37 year hold on power.