Pirelli boss Mario Isola fears the tyre supplier could be challenged to slot in 25 testing days into next season's schedule as it prepares for the introduction of 18-inch wheels in 2022.
Pirelli had planned 25 days of testing this year in collaboration with all ten teams, but the program was scrapped following the onslaught of the coronavirus pandemic and F1's decision to postpone the adoption of 18-inch wheel until 2022.
F1's exclusive tyre supplier will need to validate its tyre selection and compounds at a final test with all teams and mule cars at Abu Dhabi after the end of the 2021 season.
But Isola is concerned that Pirelli may not have enough testing mileage or data behind it at that point if COVID-19 restrictions disrupt its 25-day program.
"It will be very difficult to fit the 25 days of testing in next year's calendar," Isola said, quoted by Motorsport.com.
"We know for sure that we are going to start the season with COVID restrictions still in place.
"As soon as there is a draft of the calendar, we will try to put some days in it. One option for example is to try and use as much as possible the Tuesday and Wednesday after events, so staying on the same track. This minimises the movement of the teams.
"We have to consider that quarantine will still be in place, moving from one country to another, this kind of stuff.
"We will try to do a clever and flexible plan for testing, but it is clear that without testing, we cannot introduce the 18-inch tyres, so we have to find a solution.
"It's not easy, but we will do our best, but together with the teams we will try to introduce a calendar for these criteria."
Isola also highlighted the issue of wet tyre testing, with Paul Ricard the only track equipped for wet running simulation.
"For wet testing it's difficult or impossible to test on the same circuits," said Isola.
"Other than Paul Ricard, which is the only circuit with sprinklers, or in Fiorano, but in Fiorano we don't have a Grand Prix. So for wet testing we have to make a plan that is not linked to one event."