Shares in Nissan Motor Co. have declined 2.8 percent in the past week, underperforming a rise in other Japanese car stocks, since Ghosn said a capital stake would likely be part of an alliance with GM, and that the stake would probably be big.
"We are not making a capital investment into GM as the first element or condition," Ghosn, chief executive of Nissan and Renault SA, told a news conference in Tokyo.
"This was not discussed with the GM team, and I think it is premature to talk about it."
In a meeting last Friday in Detroit, Ghosn and his GM counterpart, Rick Wagoner, agreed to begin a 90-day study of a possible three-way alliance that would be headed by experts of each potential area of cooperation from each company.
Working-level talks would likely focus on areas such as pooling purchasing of parts and sharing vehicle platforms, the CEOs have said.
"If we come to the conclusion after 90 days that the synergies are big enough to justify the efforts, then we can go to the second step, which consists of saying: what would be the best organisation and conditions -- including shareholdings -- in order to make sure the synergies happen," Ghosn said.
He stressed that the second step would only be taken if the synergies are judged big enough for all parties involved.
Analysts have warned that a tie-up might not produce the cost savings suggested by GM's billionaire shareholder Kirk Kerkorian -- the original architect of the discussions -- and could threaten to distract both CEOs at crucial times for their respective firms.
Nissan, caught in a worldwide sales slump due to a dearth of new cars, is expected to post weaker earnings in the first half of this business year, and analysts say a sufficient turnaround in the latter half is far from certain.
France's Renault is also set to see its profit margin erode this year, moving further away from a goal of 6 percent in 2009.
Ghosn acknowledged that both Nissan and Renault faced challenges in markets around the world, but added that the talks with GM should help -- not distract from -- the companies' achieving growth in the medium term and beyond.
"If there is the slightest doubt that this could be a distraction or a weakness or a threat to fulfilling the commitments (laid out for Nissan and Renault), I would not do it," he said.
Ghosn, who has been instrumental in steering the Japanese-French partnership since its birth in 1999, also said he would be open to joining the GM board if that were necessary, but not at the expense of Nissan and Renault.
Shares in Nissan shed 1.1 percent to close at 1,155 yen on Friday, while the Nikkei average ended down 0.84 percent.
Since Kerkorian first suggested a three-way alliance on June 30, Nissan's shares have fallen 7.6 percent.