"I stressed again and again in the company's executive board meetings there was no way we should pull out, although we have to drastically cut our costs," he is quoted as saying by the Yomiuri Shimbun newspaper.
"Obviously our negative business reports did cause some doubt."
Yamashina said Panasonic's decision to extend its contract as team title sponsor through to 2012 was instrumental.
"I was extremely happy that Panasonic decided to renew its contract with us even though they also had some financial trouble. Their understanding of what we are doing allowed us to keep racing," he admitted.
Nevertheless, the team's racing budget has been seriously cut back. Yamashina told Reuters, "I'm not able to put a figure on how much the budget was slashed but in all my time at Toyota I have never seen cuts like it."
With Brawn GP - formerly Honda F1 - off to a promising start, Mercedes-McLaren unexpectedly lagging behind and the rest of the grid in turmoil, the 2009 Formula 1 season could shape up to be the most exciting in a decade, even with a shrinking field and controversial new rules in place.