Honda Formula 1 boss Yusuke Hasegawa is not particularly optimistic that there is enough time to introduce its engine upgrade in Canada.
McLaren are crying out for some good news as the search goes on for their first World Championship point of the season.
Canada was expected to bring engine updates, but it now appears McLaren will have to continue playing the waiting game.
"I don't give up and we are trying very hard [to be ready] but until Thursday [before the race], I can't decide," said Honda chief Hasegawa.
"Already, we have had some performance [from the update], but if it is very small, it's not worth changing engine for the next one.
"We haven't started working on the settings. If we are not confident enough to set up that specification, it will cause some driveability issues, so the settings are also important.
"We have some other elements in development, we can introduce it if we can set up and if we can check the reliability. Everything is not ready. But we have some factors (that are).
"Maybe we stick with the next step of the engine, even if the next step up is very small, or can we try another step up in performance? It's very tight to introduce a big update for Canada."