Venezuelan President Hugo Chavez’s revelation that Cuban doctors must remove a possible malignant tumor has thrown his drive for reelection into doubt, raising questions about whether a man famous for his stamina can withstand the rigors of a tough campaign.

“In the coming weeks, unfortunately you will not see me, unfortunately I say it, and I say it with much pain,” Chavez said in a long phone interview with Venezuela’s main state television network that aired Tuesday night. “It’s the truth. I will not be able to continue at the same rhythm.”

The disclosure, after months in which Chavez insisted that he was cancer-free, prompted Venezuelans to wonder Wednesday whether he would be able to sustain a high-energy campaign of the type that has characterized his rule over the past 13 years. Some political analysts even speculated that he might be forced to drop out, creating a power vacuum in a country where the president’s personality-based reign has meant there is no logical successor.

“It creates a very complicated and uncertain political situation that I think helps the opposition in a really unprecedented way,” said Cynthia Arnson, director of the Latin America program at Washington’s Woodrow Wilson Center. “It’s Chavez and his personality and his charisma that have held his movement together.”

The president’s delicate health returned to the headlines after Chavez said he will soon return to Cuba for surgery to remove what he called “a lesion” that could be malignant.

“If it turns out to be malignant, well, that opens a new phase of radiation therapy that would be more focused,” Chavez said. “That will stop me, stop me, of course.”

His comments in the phone interview, along with an earlier announcement Tuesday, come at a difficult time for the ailing 57-year-old leader. The populist firebrand, who delights in taunting the United States, is in his toughest of three reelection battles.

This time, his opponent is a popular governor, Henrique Capriles, who has shown himself to be adept on the campaign trail. At just 39, Capriles presents an image of youth and vigor that stands in increasing contrast to the picture of a president hobbled by serious illness.

On Feb. 12, more than 3 million voters turned out to overwhelmingly select Capriles as the opposition’s candidate for the October elections from a field of anti-Chavez foes. His emergence has flustered Chavez, who has referred to Capriles as “a low-life pig” and “the loser” and depicted him as a pawn of the United States.

“The contrast between the two couldn’t be more dramatic: a young, telegenic Capriles against Chavez, who looks worse all the time,” Arnson said. “This can only help the opposition on the media front.”

The president’s condition also highlights the inherent weakness of a government in which Chavez’s power is unrestricted and uncontested, said Demetrio Boersner, a political analyst in Caracas. “All the powers are concentrated in his hands, so if he’s out, then the whole system starts to weaken,” Boersner said.

Boersner said that rivalries among Chavez’s associates could begin to percolate while the president’s followers question whether the movement would survive without him. “The people will be more realistic, evaluate the proposals from Capriles, consider the bad government of Chavez and the real situation in the country,” Boersner predicted.

In Venezuela, the president’s health has been a state secret since Chavez announced last summer that doctors in Cuba had removed a baseball-size tumor from his pelvic region.

The president later said he had recovered completely after four chemotherapy sessions that led to hair loss and caused his body to swell. But he never disclosed what kind of cancer he had or exactly where the tumor was located.

On Tuesday, Chavez offered contradictory comments about his health.

Earlier in the day, wearing a red hard hat and talking to state television during a factory visit, he said that there was “no metastasis” and that rumors of his ill health were being spread by his political enemies. “No one should be alarmed,” he said.

But later, in the phone interview on state television, Chavez signaled that he might be out of sight for a few weeks.

“I am obligated to attend to this new circumstance, to rethink my personal agenda, and take care of myself and confront what has to be confronted,” he said.

Michael Pishvaian, an oncologist at Georgetown University’s Lombardi Comprehensive Cancer Center, said the new developments are “ominous.”

“I think we can pretty safely say that this is a cancerous tumor that has recurred,” said Pishvaian, who has no direct knowledge of the case but has been following the turn of events in Venezuela. “Anytime there’s a local recurrence of a cancer, particularly after he’s had chemotherapy to kill residual cancer cells, it means that those cancer cells were resistant to the cancer therapy and are back.”

Pishvaian said that after surgery, Chavez could undergo anywhere from 10 to 40 radiation therapy sessions over as many as six weeks. Those sessions can cause complications such as nausea, diarrhea and fatigue.

The oncologist said that Chavez may be able to carry out some of his duties as president but that campaigning would be a challenge. “He may not be able to withstand the real rigor of a campaign,” Pishvaian said.

In the phone interview, Chavez tried to sound upbeat while reflecting on his hopes for the future.

“I ask for life,” he said, speaking to his followers. “I want to live with you and fight with you until the last moment of this life that God gave me.”