"Opel is not for sale. GM supports it fully," said GM Vice Chairman Steve Girsky.
"It is a fully integrated part of the GM group and it is vital for the group's future success in Europe," Girsky said.
The comment was a response to an article in the Italian daily Il Sole 24 Ore that said Fiat Chief Executive Officer Sergio Marchionne was preparing a bid for Opel, ANSA reported.
GM did put Opel on the market in 2009, the year it declared bankruptcy. That effort was dropped, however, as German unions and politicians voiced their concerns over the possibility of job losses.
At the time, Fiat put in a bid for Opel, the brand produced in partnership with the French automaker PSA Peugeot-Citroen.