Romain Grosjean's one-off return to Formula 1 following his fiery crash at last year's Bahrain Grand Prix has been postponed.
The Frenchman, 35, had been scheduled to test for Mercedes at France's Paul Ricard circuit next week.
Mercedes said on Wednesday that the test had been "postponed because of travel restrictions and quarantine requirements".
The team said they were "committed" to the plan and working to reschedule it.
The original plan had been for Grosjean, who now races in IndyCars in the US, to do a demonstration run at his home grand prix before testing two days after the race.
But the demo run had to be scrapped when the French race was moved forward by two weeks following the cancellation of the Turkish Grand Prix, which itself had replaced the Canadian event.
Mercedes had still planned to allow Grosjean to test on Tuesday after the rescheduled French Grand Prix this weekend. But this has proved impossible because of the difficulties of getting Mercedes personnel into France under current Covid restrictions.
As the test is not a race weekend, the team do not have the usual travel exemptions that apply to race staff working at a world championship event.
The test, planned to be in Lewis Hamilton's 2020 title-winning car, honours a pledge made by Mercedes motorsport boss Toto Wolff as it became clear the crash would end Grosjean's F1 career. The driver described it as a "special opportunity".
Grosjean survived 30 seconds in an inferno after his car penetrated and became stuck in a crash barrier on the first lap of last November's Bahrain Grand Prix.
He extricated himself from the car and has won widespread acclaim for his bravery and presence of mind, as well as his determination carry on with his career.
He said in the immediate aftermath of the crash that he did not want his career to end in that fashion.
But he was unable to go through with a plan to return for one last race for his former Haas team at last year's season finale in Abu Dhabi because the burns on his hands were still too raw.