Venezuelan Maldonado, who brings substantial sponsorship from state oil company PDVSA, and Britain's Palmer were both signed before Renault last week publicly confirmed their plan to return as a constructor.
"The contracts have been agreed with Renault," Carter told Reuters after attending a High Court hearing involving Lotus and the British tax authorities.
"No decision has been made on a third driver, so whether or not they have someone French maybe lined up for that role I don't know," he added.
Palmer served as reserve this season and will replace Romain Grosjean in the race seat after the Frenchman moved to the new U.S.-based Haas F1 team.
When announcing the French carmaker's decision, Renault's chief executive Carlos Ghosn said that more details about "the aims, the drivers, the strategy and the partners" would be revealed in January.
That was interpreted in some quarters as raising a doubt about the existing lineup but Carter doubted that was the intention.
"As we all know, contracts can be broken if parties particularly want to, but they have both got contracts and therefore I think in January it's just going to be an announcement of everything," he said.
"I think there's going to be team name, driver lineups, colours of car or sponsors etc.
"Pastor and his funds are part and parcel of Renault's plans certainly for the next 12 months. I think the two drivers will be as we think," he added.
(Reporting by Alan Baldwin, editing by Ian Chadband)
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