An Isuzu spokesperson declined to elaborate.
A Renault spokeswoman, Christine LaVoie-Gagnon, said the French carmaker is talking with "a Japanese maker" to buy diesel engines for the luxury model, which replaces the Safrane in 2002.
Outsourcing the diesel engines "will be more economical" for Renault than producing them, she said.
She would not say how many engines Renault is seeking, but the Nihon Keizai Shimbun newspaper reported that Isuzu will supply between 10,000 and 20,000 a year.
Isuzu earlier won a contract to supply the same engine to Saab Automobile AB, beginning this month.
Supplying diesels to other automakers is a key part of Isuzu's plan for offsetting the drag of its slumping truck business in Japan and returning to profitability. The company, in which General Motors has a 49 percent stake, lost more than $500 million in the fiscal year that ended March 31.
Renault also will source 3.5-liter V-6 gasoline engines from Nissan Motor Co. for the Vel Satis.
Renault owns 36.8 percent of Nissan.