Venezuela's National Assembly has re-elected the incumbent Diosdado Cabello as a possible stand-in for President Hugo Chavez, who is in Cuba following cancer surgery.
Opposition leaders are calling for new elections if President Chavez cannot be sworn in for his new term on Thursday.
In such a situation, Mr Cabello would become caretaker president pending the outcome of the vote.
By choosing Mr Cabello the legislature cemented the combative ex-soldier's position as the third most powerful figure in the government, after Mr Chavez and Vice President Nicolas Maduro.
Thousands of the president's red-clad supporters gathered outside parliament hours before the vote, many chanting: “We are all Chavez! Our comandante will be well! He will return!"
If Mr Chavez had to step down, or died, Mr Cabello would take over the running of the country as Assembly president and a new election would be organised within 30 days.
Mr Chavez's heir apparent, Mr Maduro, would be the ruling Socialist Party candidate.
Mr Chavez, who was diagnosed with an undisclosed form of cancer in his pelvic area in mid-2011, has not been seen in public nor heard from in more than three weeks.
Officials say the 58-year-old is in delicate condition and has suffered multiple complications since the 11 December surgery, including unexpected bleeding and severe respiratory problems.
Late on Friday, Mr Maduro gave the clearest indication yet that the government was preparing to delay Mr Chavez's inauguration for a new six-year term, which is scheduled for Thursday.
Mr Maduro said the ceremony was a "formality" and that Mr Chavez could be sworn in by the Supreme Court at a later date.
The opposition says Mr Chavez's absence would be just the latest sign that he is no longer fit to govern, and that new elections should be held in the South American OPEC nation.