If Chavez is unable to be sworn in, it creates a leadership vacuum that must be filled by the National Assembly president, and the possibility of new elections arises, Capriles said.
Cabello has said that he has no intention of assuming power if Chavez is not sworn in.
"When (the opposition) talks about a power vacuum, they are proposing a coup," Cabello said, the state-run AVN news agency reported.
Maduro: 'The popular will is what prevails'
The government says that Chavez's new term begins automatically because he was re-elected and that the inauguration could be held later.
In remarks broadcast on national television Tuesday night, Vice President Nicolas Maduro said the inauguration date "is a formality."
Speaking to Venezuela's military leaders, he said that declaring Chavez temporarily absent from his post "would be crazy because the popular will is what prevails."
Voters have re-elected Chavez, he said, calling on the military to help continue Chavez's revolution.
There is no such automatic continuity of power, Capriles said, arguing that "the only thing that has continuity are the country's problems."
"If the constitution is not followed, or there is a conflict of interpretation, the Supreme Court has to take a position," he said.
Capriles expressed concern about unrest or political crisis in the absence of a decision by the high court.
Chavez has not been seen in public and officials have not released any photographs of him since he arrived in Havana for his fourth cancer operation in early December, fueling speculation that his health is worse than the government is letting on.
Last week, a government spokesman said Chavez was battling a severe lung infection that has caused respiratory failure. Ernesto Villegas said the president was following a strict treatment regimen for "respiratory insufficiency" caused by the infection.
His condition remained unchanged Monday, the government said in a statement.
"Treatment has been administered permanently and rigorously, and the patient is supporting it," the statement said.