Charles Leclerc of Ferrari (C) enters turn one during the Formula 1 Australian Grand Prix 2022 at the Albert Park Grand Prix Circuit in Melbourne, Australia, 10 April 2022. EPA-EFE/JAMES ROSS AUSTRALIA AND NEW ZEALAND OUT A well-placed source confirmed to Reuters that the news, first reported by the Daily Telegraph and Sky Sports television, was correct.
A spokesman for the governing FIA said medical information about its personnel could not be disclosed "unless it is relevant to the running of an event".
Sky said it understood both men had tested positive after last weekend's Emilia Romagna Grand Prix at Italy's Imola circuit.
Travel to the United States currently requires a negative test taken no more than a day before departure, regardless of vaccination status.
Practice for the May 8 race starts on Friday, May 6.
Portuguese Freitas and German Wittich were appointed in February as alternating replacements for now-departed Australian Michael Masi following a review of last year's controversial season-ending race in Abu Dhabi.
Masi changed safety car procedures late in the race, a decision that effectively handed the title to Red Bull's Max Verstappen.
Should neither race director be available for the race at the Hard Rock Stadium, other options could be British veterans Herbie Blash and Colin Haywood.
(Reporting by Alan Baldwin, editing by Toby Davis)