Pirelli says it faces a "big challenge" to prepare low-degradation Formula 1 tyres for the 2020 season as it has just one remaining '19 test to work on its rubber.
Its 2020 test programme - so far involving nine teams and four sessions in Bahrain, Spain, Austria and Silverstone - had been focussed on previously agreed aims to create a wider working range and less overheating.
But recent meetings regarding future rules have put a new emphasis on low degradation, with the drivers particularly keen to have tyres with which they can push harder for longer.
Pirelli now has just a single test session - with Mercedes at Paul Ricard on September 12-13 - in which to track test low-degradation tyres.
It then must provide the definitive 2020 product for all the teams to test in the week after the Abu Dhabi race.
The specific requirements for the tyres will be formalised in a target letter, which Pirelli hopes will be agreed by all parties over the Hungarian GP weekend.
Pirelli F1 boss Mario Isola admits that the new focus on low degradation when Pirelli's 2020 test programme was nearly complete has not made things easy for the company.
"It is different, because we were talking about overheating reduction, and wider a range, but reducing the level of degradation is something that is new," he said.
"I'm not 100% sure that we have what they are looking for in our range of possible compounds, and in that case, we have to develop something new.
"We only have one session for 2020 tyres, in the middle of September in Paul Ricard.
"It's a big challenge, so hopefully we are already going in the right direction with the development we have made so far, but we need to be 100% sure.
"One session is not a lot. Let's go step by step.
"Now the most urgent thing is to close the target letter, then to validate the development in September, and then we come to a conclusion."
Isola explained it was crucial for Pirelli that the target instructions specified exactly what it needs to produce for 2020.
"The general consensus [now] seems to be on low degradation tyres," he said.
"[But just the words] 'low degradation' is not enough for us - it could be low degradation for me and not for you, for example - so we need to understand which is the number of low degradation.
"Also the delta lap time that is expected between different compounds.
"If there are no modifications in the sporting rules for next year it means that we are going to bring three compounds to each event.
"We need to know which is the expected lap time between the three compounds, the level of degradation, a reduction in overheating [request] is coming from the drivers, and a wider working range.
"Those are the main targets for next year. Isola says the new target letter will be more specific than its predecessor, with which the tyre company has been working for the past three seasons.
"With the experience of the old one we are making some integration in the target letter to be more precise," he said.
"Being more precise means that we have more clear targets, and then we will do our best to achieve all the targets."