Christian Klien will stand in for Sakon Yamamoto at Hispania this weekend as the Japanese driver is suffering from illness.
Team boss Colin Kolles confirmed that the arrangement was a one-off for Singapore and that Yamamoto would return to the seat at Suzuka provided he was healthy.
"It looks as if Sakon Yamamoto has food poisoning and he doesn't feel well," Kolles said.
"Because of this, Christian Klien will be driving the car this Friday and the rest of the Singapore Grand Prix. I hope Sakon gets well soon and is able to drive at his home Grand Prix in Japan."
Klien has already driven the Hispania in Friday practice at the Spanish and European Grands Prix. This weekend will be his first Formula 1 start since the 2006 Italian GP, which was his final appearance for Red Bull. He had driven in 46 races for Jaguar/Red Bull since joining the team in '04, taking a best finish of fifth at Shanghai in '05.
Since losing his Red Bull seat, Klien has filled test and reserve driver roles with Honda, BMW and this season Hispania, and was also part of Peugeot's Le Mans programme before deciding to focus solely on his F1 ambitions in 2010.