Venezuelans will vote on Sunday in a primary to choose a unity opposition candidate to face President Nicolas Maduro in his probable re-election bid next year, amid pledges by the United States to roll back sanctions relief if the government fails to lift bans that prevent some opposition figures from holding office.
But Machado, like two former rivals who dropped out of the race, is barred from public office over her support of the sanctions on Maduro's government and would not be able to register for the general election.
The opposition and government this week signed a deal on some election guarantees, including the presence of international observers. The accord allows each side to choose its candidate according to internal rules, but did not retract the election disqualifications.
The United States, which broadly eased Trump-era sanctions on Venezuelan oil and gas and bonds in response to the deal, has said Maduro has until the end of November to begin rescinding the bans and releasing political prisoners and "wrongfully detained" Americans.
Some in the opposition have said they are skeptical Maduro will follow through on the deal.
The opposition, which says the disqualifications are unlawful, has been reticent to confirm what it would do if Machado wins the primary but is unable to compete in 2024.
Machado - who says her goal is to remove Maduro in a fair and peaceful vote - has said she could pressure the electoral authorities to let her register. Maduro has not announced that he will seek re-election, but many observers expect him to run.
Others have argued selecting a substitute candidate would be necessary, though whether the often-fractious opposition would accept Machado choosing a replacement remains to be seen.
All of Venezuela's 20 million voters can participate in the primary, which is being organized without state help.
Ten candidates - including former lawmakers Carlos Prosperi and Delsa Solorzano - will compete.
Polling places - including many private homes - number 3,010 locations. Abroad, Venezuelan migrants can go to voting centers in 28 countries to cast ballots. About 4 million Venezuelans living outside their country are thought to be of voting age.
