Formula 1 is still nervous about the ongoing impact of coronavirus, Mercedes boss Toto Wolff admits.

As it emerges that George Russell's trainer is in isolation with symptoms, F1 was already digesting the news that a limited crowd of 13,000 spectators per day have now been excluded from this Imola race weekend.

"Yes, the situation is becoming more difficult," Wolff said on Friday.

"Formula 1 does not put anyone in danger as we are staying in our microcosm, but we also cannot ignore that the number of cases in various countries is growing rapidly.

"At some point the leaders of these countries may decide to close the borders which may affect our plans here in Formula 1."

In the paddock on Friday, the subject of F1's provisional 23-race calendar was a hot topic, with many believing the unprecedented number of races is too great a burden for the sport's travelling staff.

"As of now, Chase Carey has assured us that the schedule remains in place," Wolff said.

"But he also said that against the backdrop of a progressing pandemic, no one knows what the situation will be in a week, let alone a month."

Haas boss Gunther Steiner agrees: "First you need to plan everything you want to do, and then adjust it as necessary.

"If we just wait for the pandemic to completely subside, we will not be able to do anything as it may drag on for years.

"But we are becoming smarter, learning to cope with this and perhaps a vaccine will come, but there are so many different assumptions that there is no point in talking about it," he added.