Šarec, whose LMŠ came second in the election after Janez Janša's right-wing Democrats (SDS), added for the press ahead of today's maiden session of parliament that he expected Tonin to resign in case the final result of the ongoing coalition talks would require this.
According to Šarec, Tonin will be put forward as speaker candidate by the LMŠ, the SocDems, the Pensioners' Party (DeSUS), the Modern Centre Party (SMC), the Alenka Bratušek Party (SAB) and the NSi. Together they have 50 votes in the 90-member National Assembly.
While indicating the contours of a possible coalition, the move is far from cementing it, as recent statements by MPs suggested that coalition building is progressing only slowly and that the speaker that needs to be appointed at the maiden session could well only be temporary.
This was echoed by Tonin, who said he had received the support in writing from the listed parties as well as the oral support of the SDS and the far-right National Party (SNS).
The only party not to express support to him was the far-left Left, whose inclusion into a centre-left coalition would be an alternative to the NSi's.
"I'm aware that my role is temporary. I will above all make sure that the parliament is constituted in a smooth fashion," Tonin told the press.
NSi MP Jernej Vrtovec said earlier the NSi was trying to "cut the Gordian Knot to overcome divides, especially ideological ones and see what is good for the people and country". He however stressed that the NSi's participation in ruling coalition would depend on the ongoing talks.
The outgoing Prime Minister and SMC head Miro Cerar also told the press it was of key importance that "the first, determined steps are made towards forming a stable centrist coalition".
He added that such a coalition was being indicated today and that this would make things easier for Šarec in the ongoing talks.
Cerar, who had been among the potential candidates for speaker along with current speaker Milan Brglez, also of the SMC, said his party would remain constructive and would not insist on proposals that would undermine the path to an agreement.
He described the joint support to Tonin as "an expression of great trust", saying Tonin had made assurances that he only wished to be temporary speaker and that a final agreement "on how to represent certain content at certain posts" will have to be reached once the coalition is formed.
Support for Šarec's Tonin proposal - Šarec tops the list of signatories - was also expressed by SAB MP Marko Bandelli, who called for a centrist government, as well as by DeSUS deputy group head Franc Jurša.
Jurša believes that Tonin, despite only being 34, will know how to run parliament "in the period meant for him".
Matjaž Han of the SocDems, who said he intentionally did not use the word temporary when speaking about the likely new speaker, said that Slovenia was in a position where a purely left-wing or purely right-wing government was not possible.
Han, who said the coalition talks can start in earnest now on Monday, rejected the view that Tonin's nomination meant a defeat for the left bloc, saying the left-right divide was poisoning the country.
Janša only responded to the developments via Twitter in what was a reaction to a tweet by Aleš Zalar in which the former left-leaning justice minister suggested the centre-left bloc was in fact helping form a Janša-led government in a repeat of developments in 2011.
"Not yet. For now we are only solving the deadlock of the so-called left, which is only able to agree on somebody who is not theirs. We are doing this so that parliament can start working normally. Problems are accumulating even though the MSM are hiding this," Janša tweeted.