Lewis Hamilton believes Red Bull is “quite a bit ahead” of Mercedes heading into qualifying for the Azerbaijan Grand Prix.
Hamilton showed signs of closing the deficit to Ricciardo but aborted fast laps due to driver errors in Practice 2.
His team-mate Valtteri Bottas was fourth having set a lap a tenth faster, but Mercedes found themselves significantly behind Ricciardo, Kimi Raikkonen (Ferrari) and Max Verstappen, who was third in the sister Red Bull.
“I did anticipate it would be very close coming into this weekend obviously from the previous race experiences,” said Hamilton.
“It's been a smooth day. We got through everything we needed. I did all the laps, not really many mistakes and (we gathered) lots of information.
“We are not quick enough. Red Bull is definitely quite a bit ahead and I couldn't match their time today so we have some work to do.”
“They are both currently ahead still as they were in the last race but more so today. Red Bull seems to have picked up quite a bit of pace so we shall see.
“I'm hoping overnight, I'm going to be knocking on the doors of all the engineers, pushing them, and hope I can get them to make some changes.”
Although happy at the pace he delivered in practice, Ricciardo expects rivals Mercedes and Ferrari to show more pace in qualifying.
“I think we can still find a little bit more but generally I was happy and I think it's going to be quite a close battle tomorrow and Sunday,” said Ricciardo.
“The car feels really strong through the castle section in the second sector and I felt comfortable and confident there.
“It's a very tight part of the circuit but that's the place that I felt most comfortable and the RB14 felt strong.
“I'm sure the others will turn it up a bit in Qualifying and gain in sectors one and three but sector two will be the key for us.
“It is encouraging even if we don't qualify on the front row tomorrow as I think the race car will be very strong. We are still in the group of favourites.”
Qualifying for the Azerbaijan Grand Prix is scheduled to begin at 2300 AEST on Saturday night.