HRT have been left off Formula One's official entry list for next season, increasing concerns the Spain-based team will fold.
The FIA published the 2013 championship entry list on its website on Friday after the deadline to pay next year's F1 registration fees with HRT being the notable absentee.
HRT had to pay $US 500,000 to enter the 2013 F1 championship but with owners Thesan Capital keen to sell, the fee has yet to be paid as the team continues to look for buyers.
Formally known as Campos Meta 1 and Hispania Racing, HRT have failed to earn a point in three F1 seasons, with Pedro de la Rosa and Narain Karthikeyan driving for HRT in 2012.
Karthikeyan produced HRT's best result of 2012 when he finished 15th in Monaco.
The last F1 team to drop out of the championship was Japan's Super Aguri in 2008.