Both Sauber and Toyota are missing from the FIA's newly published provisional entry list for the 2010 season.
The list features 12 teams, with a final and thirteenth likely to be added ahead of talks preceding the World Motor Sport Council on December 11.
There has been speculation that, in order to avoid a $150m fine, Toyota has been in talks with a Serbian outfit called Stefan GP about handing over its commitment to the Concorde Agreement.
Sauber, presently on standby should a vacancy arise, will be re-acquired by its founder Peter Sauber only if the FIA grants it an official entry.
The Swiss newspaper Blick said Sauber, 66, was meeting with Bernie Ecclestone on Monday.
The FIA said Toyota "remains formally bound by the Concorde Agreement to put forward a team for participation, though it has indicated that it will not be in a position to do so.
"An announcement will be made regarding this entry in due course."
Sauber told F1's official website: "Regarding the slot on the grid I am very confident that we will be given a final confirmation very shortly."
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Formula 1