"Of course you never stop hoping," De Telegraaf newspaper quotes Ricciardo as saying in China, "but over time these things reduce the optimism."
The Australian, who is out of contract late this year, is referring to the pre-qualifying engine change his car underwent ahead of qualifying, following practice problems.
Red Bull is already considering a switch to Honda power for 2019, while Ricciardo could leave the team altogether.
"The winter tests looked a lot better in terms of reliability," Ricciardo said. "We did not expect to be in this situation in the third race, after the problems here and also in Bahrain.
"We haven't had a clean start, but now we need to get it under control."