Ricciardo was culled from the session at the end of Qualifying 2, recording just the 13th-best time of the segment.
By contrast, his RB team-mate Yuki Tsunoda did progress to Qualifying 3 and will start Sunday’s race from eighth.
“I had a lot of energy going into qualifying,” Ricciardo admitted.
“I certainly feel a bit zapped now because the result’s not good enough and it’s not where I think I can be.
“But, obviously, I’m not disappointed with the way I drove. It just simply wasn’t getting the most out of it where I needed to.
“Of course, I can say tyres felt this and that, but I need to try to understand what I was doing differently to Yuki.
Secure your spot today.
“It doesn’t change the results. Just have to suck this one up.”
Ricciardo demonstrated reasonable pace in Qualifying 1, progressing with ease with the 11th best time.
However, as has happened previously this season, he wasn’t able to improve in line with the field.
“It was weird. I think actually Q1 went relatively well, we got through and we were P11 or something, obviously close to what would have been a shot at Q3,” he reasoned.
“In Q2, everyone was able to go on a first-time lap and it felt that was what everyone was converting to and making the tyre go and work and then, for me personally, I struggled to get everything out of the tyre on the first lap.
“I was able to find maybe three-tenths, but everyone else was able to find whatever it was – six or seven-tenths.
“That was where I struggled, especially when I got to the tight stuff in the middle sector, I was honestly struggling with the front.
“I felt like I needed to be quite quick on the out-lap to get the front going, but then I was quite a bit quicker than Yuki on the out-lap and I was still struggling with that.
“So, not really sure.
“Just frustrating because here it’s so important to qualify [well].
“It was fun; it felt good, but obviously, it takes the fun out of it when you’re not quick enough.”
Ricciardo explained the problem occurred on turn-in, where he didn’t feel the grip he expected.
“As soon as I got into Turn 5, as soon as I slipped the tyre, I just feel like it really falls away,” he explained.
“With my experience, that feels like the tyre’s not quite hot enough, has not got enough energy going through it.
“I was really trying to do that on the out-lap but clearly some others were going slower and then still making it work.
“That’s where I’m a little bit puzzled at the moment by why I was still struggling there.
“It started at T5. Push, then get a snap, and then that whole section just becomes a bit of a mess,” he added.
“That’s where I felt probably that little bit of time I needed to maybe have a shot at Q3 got away from me.”
While Ricciardo will start 13th, compatriot Oscar Piastri will start from the front row for Sunday’s race.
The Monaco Grand Prix begins at 15:00 local time (23:00 AEST).
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