Talk of an initial public offering for General Motors by the second half of next year is so premature as to border on the ludicrous, a former director has said.

"It's the dumbest thing in the world to be talking about an IPO right now," former GM director Jerry York told the Reuters Autos Summit in Detroit. "It's time hopefully will come and when the time is here we'll all know it."

The US Treasury now owns over 60% of the automaker after pumping about US$50bn into its restructuring andanalysts have said an IPO could be a way for US taxpayers to recoup their investment over time.

It stands to lose one to two percentage points of market share from its current level of 19 to 20 percent, as a result of the reduction in the number of brands it sells, York said.

"They're not going to be able to make up all the volume that they had with the four brands they are shedding with four brands they are retaining," the 71-year-old adviser to billionaire investor Kirk Kerkorian was quoted as saying.

But he added: "They've done a lot of the right things and we'll all know in another six to nine months whether they need to do more structurally."