The deputy, who co-chairs the Greens/EFA group in Parliament, is also still a declared candidate for the presidency of the European Commission.
A protracted summit of EU leaders was due to resume on Tuesday in a bid to resolve the wrangle of who gets the Commission post.
The summit started on Sunday but leaders have, so far, been unable to reach agreement.
A new favourite is Dutchman Frans Timmermans, a current EU Commission Vice President.
Speaking at a news conference in Parliament in Strasbourg on Tuesday, Parliament’s spokesman Jaume Duche Guillot said MEPs are due to vote on the new presidency post at their plenary at 9am on Wednesday.
He said the process had been extended “because the political groups felt they needed more time to debate the possible candidates for the presidency.”
He said the cut-off date for nominees has now been extended to 10pm on Tuesday.
"It cannot be up to the Heads of State and governments to decide on who should be the next President of the European Parliament; it's up to the Parliament and only the Parliament to decide on our President for two and a half years” Ska Keller MEP
“The groups have until then to put forward candidates for the post,” he said.
Meanwhile, Keller said late on Monday that, as well as being a contender for the Commission post, she is now also her party’s nominee for the parliamentary presidency, currently occupied by EPP member Antonio Tajani.
She is just one of three declared candidates for the post. The others are Jan Zahradil, from the ECR group, and Sira Rego, from GUE.
Neither of Parliament’s two biggest groups, the EPP and the Socialists, have yet put forward a candidate even though MEPs are due to vote on the presidency issue on Wednesday morning.
Speaking on Monday, Keller said, "It cannot be up to the Heads of State and governments to decide on who should be the next President of the European Parliament; it's up to the Parliament and only the Parliament to decide on our President for two and a half years.”
"These elections proved that European voters want change in the EU. With the high turnout in the European elections, the Parliament has a special role and responsibility as the only directly-elected EU institution to make the voters' voice heard. Its role vis-a-vis the Council and the Commission needs to be strengthened.”
"I want to make the European Parliament more democratic, open and transparent. We need to make the Parliament the champion for the rule of law and democratic principles.”
“Our goal is to bring the inspiration and momentum of these social movements into the European Parliament,” Sira Rego MEP
“In order for the European Parliament to be fully credible, it must act upon the principles that we publicly defend: we need to establish a new understanding of transparency and openness to the European public – be it when it comes to the publication of key documents of legislation or the influence of lobbyists on the legislative process," Keller added.
Speaking of her candidacy for the same job, Rego, a Spanish MEP, said, “We see our candidacy to the presidency of the European Parliament as an opportunity to lay down our proposal for a completely different model of European integration and the role of the Parliament in it.”
Elected as an MEP in the European elections in May, Rego had previously worked on energy and sustainability issues at a local level - both of which, she believes, are “fundamental for the Left in Europe.”
“Coming from Spain, a country faced with an immense struggle against the EU’s neoliberal policies, it is also where the feminist movement has been amongst the strongest in Europe.”
“Our goal is to bring the inspiration and momentum of these social movements into the European Parliament,” Rego noted.
As a member of the Izquierda Unida party, she was elected as part of the Unidas Podemos list of candidates to Parliament.
“We will decide our candidate tonight. We have no candidates for the moment” EPP spokesman
She added, “My election is an example of the unity between different leftist, environmentalist and feminist organisations and activists which will be the basis of our work in the upcoming years.”
Later on Tuesday, GUE will launch its 10 key policy demands for the EU’s new top job holders. Rego is also due to give a news conference where she will present her party’s demand for a climate emergency special committee.
On Tuesday, an EPP spokesman told this website, “We will decide our candidate tonight. We have no candidates for the moment.”