Verstappen could only finish seventh in the second Formula 1 practice session at the Sochi Autodrom on Friday, lapping over 1.5 seconds off pace-setter Valtteri Bottas' best time.
It was a session that saw a number of drivers suffer spins and lock-ups, including Verstappen, who spun during his second qualifying simulation.
The Dutchman said after practice that Red Bull knew the Sochi Autodrom was not a track that suited its RB16 car, prompting it to try various different set-up approaches through Friday.
"We know that this track is not the best for us, but we were also trying out some downforce levels and seeing what is the best option," Verstappen said.
"[In] FP2, yeah, I think we could have done a bit better, but again, we were testing a few things out. Some worked, some didn't, so it gives us a few ideas for tomorrow."
Mercedes drivers Bottas and Lewis Hamilton finished more than a second clear of the field as Daniel Ricciardo took third place for Renault, leading the battle to be best of the rest.
Verstappen said he thought it would be difficult for Red Bull to beat Renault and be Mercedes' nearest challenger in qualifying, but had higher hopes for the race.
"It will be tough in qualifying to be in P3," Verstappen said. "In the race, it looks a bit more competitive, so I'm happy about that, but there's still a bit of work to do to make sure we are still P3.
"So far today, [Renault] have been very competitive, and you never know who else.
"First of all we have to look at ourselves and make the right trade off with downforce levels as well, make sure the car is stable, and then I'm quite confident that qualy will be tight, but I think we can be in the fight."
Red Bull teammate Alexander Albon could only finish FP2 12th fastest, but said he "knew it was going to be hard" for the team in Sochi.
"The midfield have obviously made a big step since last year, so it's a bit more tight," Albon said.
"[The car] didn't feel bad, it's just everyone is very fast. We need to do some homework and find out where we can gain those little bits.
"On a track like this, honestly, it's just about looking after the tyres. It's so thermal here.
"You just need a really good balance, so if you're good in a short run, you'll be good in a long run. We're just missing a little bit in both."