Venezuela informed the United Nations Monday that Hugo Chavez, the country’s president, will not address the General Assembly in New York this week, adding speculation about the leader’s health as he battles cancer.

The email was sent from the Venezuelan Mission to the U.N. and did not specify why Chavez, 57, could not attend the meeting. But the email said he will be replaced by the country’s foreign minister, Micolas Maduro Moros.

Meanwhile, the socialist leader underwent his fourth round of chemotherapy in Cuba, describing the treatment as “highly successful.”

Reuters reported that Chavez, dressed in a blue and white tracksuit, told supporters last week at Caracas's Maiquetia International Airport that his vital signs were very positive.

“We can say, thanks to these results, that we have finished the chemotherapy cycle," he said, according to Reuters.

His specific type of cancer has not been disclosed, but he reportedly had surgery during the summer to remove a baseball-sized tumor in his pelvis.

Last week, Chavez received some support from his ally, Bolivian President Evo Morales, when Morales refused to answer health questions from reporters during a press conference and went on to say he had a conversation with his “dear friend” who was “most alert.”

“Chavez and Fidel (Castro) will always lead the revolution against the imperialists," Morales said.