Ginetta will not participate in this month's World Endurance Championship round at Austin, leaving just three LMP1s on the entry for the American round.
The British marque's pair of AER-powered G60-LT-P1s are absent from the latest version of the entry list for the 'Lone Star Le Mans' race.
No explanation has been forthcoming from Ginetta, although its cars did appear on the entry list issued for the Sebring 1000 Miles issued last week.
It leaves just two Toyota TS050 HYBRIDs and a sole Rebellion-Gibson R-13 on the grid at Austin, marking the lowest top-class car count in WEC history.
A statement from Ginetta read: "The WEC calendar is challenging, especially for any team with a new car in it's first season and we have not had the chassis' back at the factory since before Silverstone in August.
"The cancellation of the earlier WEC race in Brazil and the new race at COTA [Austin] made it impossible to do the planned work at our facility in Virginia, so the cars were shipped post race back to Ginetta UK, the cars hopefully arrive at the factory today [Tuesday]."
Ginetta's absence from the race has been partly counter-balanced by an extra entry in the LMP2 ranks from former regular WEC squad DragonSpeed.
The outfit, currently participating in the European Le Mans Series and IMSA SportsCar Championship, will field an ORECA 07 to bring up the size of the class to nine cars, and the grid in total to 30 cars.
Drivers have not been announced, but Ginetta skipping the race frees up DragonSpeed regular Ben Hanley to take part, most likely alongside bronze-rated Henrik Hedman.
Magnussen, Rockenfeller named as Corvette drivers
Corvette Racing has named Jan Magnussen and Mike Rockenfeller as its drivers for the first of its two one-off WEC outings with the brand-new mid-engined C8.R.
Both drivers were part of the Corvette programme previously but were dropped for 2020.
Magnussen was replaced in the brand's full-time IMSA line-up by Jordan Taylor, while Audi factory driver Rockenfeller was ruled out of his usual 'third man' role due to a clash between the Le Mans 24 Hours and the DTM.
It remains to be seen if either driver will have any further role at Corvette going forward. Autosport has contacted Corvette for comment.