Ferrari Formula 1 team principal Mattia Binotto says the Scuderia has ended talks over an engine supply deal with IndyCar, but series bosses remain optimistic of landing a third manufacturer.
Last May, Binotto revealed Ferrari was evaluating a possible entry to IndyCar, as imminent F1 budget caps reduced potential outlets for current staff members' expertise.
But in December, Italian sources suggested that Ferrari's evaluation was over and the decision had been made to not enter US open-wheel racing after all.
IndyCar Series and Indianapolis Motor Speedway owner Roger Penske insisted at the time that talks were ongoing, however Binotto has now poured water on the plans.
Speaking to Speedweek, he said: "After our negotiations, we came to the conclusion that we would not be joining IndyCar [in the short-term future].
"In the medium and long term, however, this option is possible. But right now we want to focus on Formula 1."
When contacted for comment regarding Ferrari's turndown and the ongoing quest for a third engine supplier to join Chevrolet and Honda, IndyCar told Autosport: "IndyCar remains excited about the 2023 implementation of a 2.4-litre, twin-turbo V6 engine with hybrid technology.
"The response from manufacturers has been very positive as we continue to discuss the addition of another OEM. The series has cast a wide net with that goal.
"Those conversations are ongoing as we remain optimistic about bringing another manufacturer - or manufacturers - into our sport."
The 2.4-litre hybrid formula was originally due to be introduced in 2022, but last October this was pushed back to 2023 in an effort to spread out costs for manufacturers and teams due to the uncertain economy caused by the COVID-19 pandemic.
At the same time, IndyCar announced a multi-year extension to its contracts with existing engine suppliers Honda and Chevrolet.
IndyCar last enjoyed three race-winning engine manufacturers in 2005 with Toyota joining Honda and Chevrolet.
Lotus joined the two incumbents for the first year of the current 2.2-litre twin-turbo V6 formula in 2012, but its powerplants were so underpowered that all but one team (HVM Racing) switched to an alternative OEM before the midway point of the year.