Ricciardo will start Sunday’s race from 18th, one place behind RB team-mate Yuki Tsunoda, as the pair struggled for pace.
RB has introduced an upgrade package this weekend which it had hoped would see it able to more seriously challenge Aston Martin.
Instead, it has been shuffled back down the order with no clear explanation as to why.
“Yesterday, it felt like, yeah, we would still try to fight it a little bit so we did make some bigger changes overnight,” Ricciardo admitted of the upgrade.
“We probably haven’t perfected it by now and maybe that’s the encouraging thing, but I feel like we did make a good job overnight to get the car in a better place.
“I felt better today, I had more confidence in it, but unfortunately on the stopwatch we’re still where we were yesterday.”
The issue, Ricciardo believes, centres on the balance of the car and the changes to that the introduction of a new floor has made.
“When you get a new floor, that’s obviously where these cars are so powerful in terms of the load and aero characteristics,” he explained.
“I felt like we made a good step today but when Pierre [Hamelin, engineer] told me P18, I think it was we ended up, I was… yeah. I didn’t really have anything to say on the radio because I was honestly quite surprised.
“I knew we were not going to be P10, but I honestly thought that would have been good enough for Q2.”
With the race unlikely to herald a significant change in fortunes, attention at RB is now centred on understanding the drop in performance.
That task will centre on learning more about the new package to determine whether the poor Spanish qualifying is a result of failing to optimise the upgraded car, or something more fundamental.
“There’s still a bit more on the package to figure out,” Ricciardo reasoned.
“That’s something obviously we’ll keep doing, but on the flipside, I do feel like yesterday we were much more out of balance and actually today, in quali, the car felt much more together.
“I actually didn’t think the car felt too bad.
“Of course, there’s some corners where you feel [you] should be flat there or whatever, so maybe missing a bit of load, but in general I felt much better than yesterday.
“So to be back where we are, I think there’s still a bit more to find.”
The Spanish Grand Prix begins at 15:00 local time on Sunday (23:00 AEST).