The MP, Marika Tuus-Laul (Center), is from one of the two coalition parties, both of which have pledged for national museum director Alar Karis.

BNS and Postimees, which belong to the same media group, both reported that Siim Kallas (Reform) would also be voting after being ferried by ambulance from hospital, where he checked in last week.

However, ERR's online news in Estonian reports that Kallas will not vote, meaning the Reform/Center bloc will be down one vote, to 58, when 68 are needed for Karis to get elected.

If neither Tuus-Laul nor Kallas voted, the two parties combined would be down to 57 votes, leaving them 11 to find from the Social Democratic (SDE) and Isamaa parties.

Neither SDE or Isamaa have thrown their lot in with Karis, the sole candidate running on Monday.

Unlike Estonia's direct elections, which permit voting online, the presidential elections are held at the Riigikogu via secret, paper ballot which must be done in person.

No proxy is permitted to cast a vote in lieu of the MP, meaning that any members not in attendance will lose their vote.

Tuus-Laul will be taken to an outdoor area within Toompea castle to cast her vote, and doesn't need to enter the Riigikogu building, BNS reports.

SDE and Isamaa leaders have both said their MPs, which together number 23, are free to vote as they wish Monday.

Since Karis is running alone, only a blank or spoiled ballot, or an abstention, would be a viable alternative to voting for him.

Early indications suggested around half of SDE and Isamaa's MPs would vote for Karis, which would be sufficient to carry two-thirds of the house and get him elected.

However, since the ballot is secret and the parties' leaderships have not stated voting for Karis as party policy – SDE in particular is more in favor of a second term for Kersti Kaljulaid – this cannot be taken for granted.

The vote starts at 1 p.m. Monday, with the result likely in by late afternoon.

Sixty-eight votes are needed for Karis to become president.

The other opposition party, the Conservative People's Party of Estonia (EKRE), has put up its own candidate, former speaker Henn Põlluaas, and can be ruled out of the equation so far as Karis votes go.

At the same time, EKRE, with 19 seats, is two votes short of the 21 needed for Põlluaas to be officially nominated, meaning he is not running on Monday.

If Monday's ballot is inconclusive, i.e. if fewer than 68 people vote for Karis, the process repeats Tuesday morning, with nominations 8.00-10.00 a.m. and the vote at noon.

Karis will be running along with any other candidates who might get nominated, and received the 21 votes needed to run.

If the second ballot draws a blank too, a third ballot takes place Tuesday afternoon as a run-off between the top two candidates by votes received, which at present would be speculative in that no other candidate has declared yet (Karis can run alone).

If that third ballot also fails to return a head of state, the process continues at the electoral college next month.

This article was updated to note ERR reported Siim Kallas would not be voting.

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