The result is a power vacuum that his camp will be hard-pressed to fill, especially if he is unable to campaign for the Oct. 7 elections or wins and then becomes physically incapable of governing.
"Venezuela is living with the unsettling effects of prolonged, one-man rule," said Michael Shifter, president of the Washington-based Inter-American Dialogue think tank. "Anything can happen."
Shifter said "a fierce power struggle and jockeying for position" is nearly inevitable for Chavez's ruling Socialist Party of Venezuela.
"I promise I will fight without respite for my life," Chavez, 57, tweeted Wednesday.
A day earlier, he said in sharing his bad news that he could be out of action for weeks.
"I'm not going to be able to continue with the same rhythm," he told state TV by telephone late Tuesday.
Chavez did not mention who might replace him during an absence that cancer specialists say could last weeks if the leader has to undergo radiation treatment, as he said he expected. Chavez said the same doctors who removed a baseball-size cancerous tumor from his pelvic region in June would be operating on him.
He denied rumors the cancer had spread aggressively, but also said his doctors don't know if the new one-inch lesion they found over the weekend is malignant.
The president of the Chavez-controlled National Assembly, Diosdado Cabello, told reporters that Chavez remained the ruling party's candidate. Chavez is expected to travel to Cuba on Friday or Saturday, Cabello said.