BOGOTA -- Just a few years ago, Venezuelan President Hugo Chávez used to taunt the opposition by vowing to stay in power until 2031. But now that the 57-year-old leader is facing another cancer scare, some analysts question his ability to hold onto the presidency through the current election cycle.

Facing a tight reelection against a unified opposition, Chávez had been stepping up his public appearances and relying on his legendary charisma to secure an additional six-year term.

Despite being in power for 13 years, he still enjoys approval ratings of about 50 percent. But the announcement Tuesday that he will be returning to Cuba to have a lesion removed, and that it’s likely cancerous, changes the equation.

While Chávez remains popular, his allies and ministers are often blamed for the nation’s problems, wrote Daniel Kerner, a Latin America analyst with New York-based Eurasia Group. And that makes Chávez’s illness — even if he is healthy enough to campaign — a serious liability.

“A large share of voters would probably be reluctant to elect a president that may not be around to fulfill his mandate, especially given how unpopular figures around Chávez are,” Kerner wrote.

After a week of rumors about his failing health, Chávez on Tuesday admitted that doctors had found a lesion or “wound” on the site where he had a cancerous tumor removed in June.

Later, he told reporters that he would be out of the public eye while he recuperates. But over the last 13 years, Chávez has become the face and force of his government — and analysts said there are few understudies to take his place.

“There is no Chávez substitute and without him, there’s no way they could win,” said Anibal Romero, a professor of Liberal Arts at the Universidad Metropolitana in Caracas. “But there’s still so much we don’t know, and that makes it impossible to extrapolate.”

Among the unknowns is how soon Chávez may return to the political scene. Doctors said it’s feasible that the lesion is benign and the president is back on his feet within days. But Chávez himself has been more cautious. On Tuesday, he said he would likely be out of public view for “weeks” and added that even when he does return he’ll have to pace himself.

That has made the issue of succession — even if it’s to serve as his proxy on the campaign trail — more pressing.

In June, when Chávez first announced that he’d been treated for cancer, rumors swirled about who would be next in line. At the time, Vice President Elias Jaua, Foreign Minister Nicolás Maduro and Chávez’s brother Adan, were on the short list.

But the political landscape has shifted over the last eight months, said Saúl Cabrera, vice president of Consultores 21, a market research firm.

All three men have faded from public view, he said. In addition, Chávez has tapped Jaua and Maduro to run for gubernatorial posts in the key states of Miranda and Carabobo — effectively, sidelining them from presidential lineup, Cabrera said.

Meanwhile, longtime ally, Diosdado Cabello, has been on the rise. Cabello, 48, was a lieutenant when he joined Chávez during a failed coup in 1992. He went on to become the governor of Miranda State and to hold a series of cabinet positions. He was also interim president in 2002, when Chávez was briefly ousted in a coup.