Paul Ricard, Spa and Sochi have emerged as possible venues for Formula 1's Saturday qualifying race experiments in 2020 - provided all the teams agree the idea can go ahead.
A change to next year's FIA Sporting Regulations at this stage requires unanimity, and Autosport understands that more than one team remains opposed to the plan for race format trials despite intense lobbying by the FIA and the F1 organisation.
But a change for 2021 will not require unanimity if made before the end of April 2020, so it is possible that the idea will be postponed and tried a year later than is currently intended.
If the experimental sprint events, which are expected to feature a reversed championship order grid, prove to be successful they will be potentially be used more extensively in the future - although not on all race weekends.
The subject has been discussed extensively in recent meetings of key stakeholders, with details further refined in a meeting of team managers and FIA and F1 representatives at Suzuka on Thursday.
A second meeting on Friday involved team representatives - mostly strategists such as James Vowles of Mercedes - discussing the results of their simulations of how Saturday races would unfold at particular circuits.
The consensus was that frontrunners would find it harder to make progress through the field in these races than they currently do when starting out of position in a normal grand prix, because there would be no pitstops and the likelihood is that everyone will start on the same tyre compounds.
A lot of thought has gone into the selection of possible venues, taking into account factors such as a pattern of uneventful races in the past.
The races chosen are the 10th, 14th and 17th rounds of next year's schedule.
That means nine events will have taken place before Paul Ricard in order to determine the world championship order that would then be reversed for the Saturday race.
There are five races to run after Russia, therefore reducing the likelihood that the Sochi weekend could prove decisive in the title battle.
The sprint races will fill the traditional Saturday afternoon qualifying slot.
Drivers will have a free choice of tyres for the start, and there will no requirement to use two tyre compounds and therefore no compulsory pitstops.
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There will also be a much shorter preamble on the grid before the start than is traditionally the case.
A concern for teams has been the extra risk of sustaining damage in Saturday races relative to normal qualifying, with the cost of having sufficient spares to hand a major talking point.
Sochi promoter Sergey Vorobyev said he would be open to the idea of hosting a Saturday race at his event when asked by Autosport.
"At this stage I cannot confirm or deny," he said.
"We support Liberty's efforts to modernise F1 and would be happy to serve as a proving ground for experiments."