Formula 1 only has "a couple of months" to open the door to a new Andretti-Cadillac team in 2025 or 2026.
That is the claim of 1978 world champion Mario, whose son Michael - who also raced in F1 - is bidding to bring his Andretti Autosport empire into the sport with General Motors' backing.
However, while FIA president Mohammed ben Sulayem is keen, the bid is facing major opposition from existing teams who fear a dilution of their value and official income.
It means that, for the moment, the Andretti bid has the brakes on.
"The truth is that we are going on structuring the team day by day, as though there was already a green light from the federation," Mario Andretti, 82, told the Italian magazine Autosprint.
"A program like this is very complex so we need to keep moving, even if it's not at maximum speed. To put key names under contract, we need certainties, so from that point of view we are still on standby," he added.
When asked how long that 'standby' period can last before Andretti needs to call off the entire program, Mario answered: "Let's say that we could reasonably have an answer within a couple of months.
"But it is also true that, at this point, every day counts. Let's wait and see, but we are now in the decisive phase."
Andretti confirms that his son's bid has had the support of FIA president ben Sulayem "from the very first moment".
"It was he who advised us to find a partnership with a great manufacturer to give more strength, bite and depth to our F1 program," he said.
"From there came the union with Cadillac, which means a commonality of intent with General Motors."
Mario Andretti also scoffed at the existing teams' arguments about why F1 should think twice about allowing eleventh and twelfth entries to race.
"Money, money ... but what money?" said the Italian-born American. "How much do the annual earnings of a big team drop if we come along?
"In a situation of exponential growth for F1, to see an American-based team with an identity deeply rooted in the racing world would only be something extremely positive for everyone," Andretti insists.
