The Hinwil-based outfit is the only team not to score points in the current campaign, having seen its qualifying performances drop since the start of the season.
«We still have work to do,» said Bottas.
«We need to keep bringing upgrades and make the car faster. It is not rocket science, we just need more bits.»
On whether an update package was on its way for the Spanish Grand Prix, the Finn replied: «We have small things but a very high downforce track, a different track to here. I think it is going to be close, as we have seen. The next step is to get back to Q2 and then we can fight a bit better.»
Valtteri Bottas, Stake F1 Team Kick Sauber C44
Photo by: Zak Mauger / Motorsport Images
His fortunes didn’t turn around in time for qualifying and with a back-row start facing him, he joined Bottas in commencing the race from the pitlane.
Eventually finishing as the only driver lapped by race-winner Verstappen, the Chinese driver conceded: «Just struggling across the different compounds. At the halfway stage of the race, I was a bit out of the race anyway, so a bit lonely.
«We have something already planned back at the factory to check everything, make sure we are starting a little bit more from scratch. These two weekends, I feel like something is not clicking right and this weekend, all these mistakes, they never happened before.
«So we try to understand all of our issues and have some plans for the next race.»
Asked if it was just the rear of the car he was lacking confidence with given his crashes earlier in the weekend, Zhou said: «It is everywhere, to be honest, just four-wheel sliding. There is not a massive limitation, we are just lacking grip. It is quite simple but not an easy one to get progress.»