Valtteri Bottas has claimed he was assured of his place as a "pillar" of the Sauber/Audi Formula 1 programme and labelled his period with the Hinwil-based outfit a "mistake".
The Finn joined Sauber for the 2022 season, when it was still called Alfa Romeo, and found some success, securing a top 10 finish in the drivers' championship.
But the team has regressed in the past two seasons and, had it not been for Zhou Guanyu's points at the Qatar Grand Prix, Sauber would have failed to score at all this term.
After his final race with the squad before what is expected to be a reserve role with former team Mercedes for next season, Bottas conceded: "It [the move to Sauber] was a mistake. But we can't predict the future.
"Everything started well off in the first year, but since then, it was downhill. But we just can't predict future, that's how it is. Just want to make sure that the next move I make is going to be a good one. Hopefully, there's better times to come."
Sauber will become the Audi works team from 2026 as F1 ushers in a new regulatory era and since Bottas joined Sauber, the project has undergone a tumultuous period.
The management structure has vastly changed, with former CEO Andreas Seidl ousted in favour of hiring ex-Ferrari team principal Mattia Binotto.
Fred Vasseur was also at the team before taking over from Binotto at the Scuderia and Bottas labelled the Frenchman as a major draw when making the move.
"Fred was a big part, there was a clear plan for targets for the three years, and also how to get there," explained Bottas. "But those plans and targets went into the bin when he left.
"We had a good relationship and clear targets and that changed a lot. I don't blame [him] because, for a team principal, if you have a chance to go to Ferrari, you go."
On whether he explored his options when Vasseur left, Bottas revealed that he was given assurances about his position in Audi's long-term planning, only for that to be proven untrue with his departure this year.
"I did have an option that if Fred goes, I can go," revealed the 10-time grand prix winner. "But I was then, once Audi was confirmed, always told I would be a pillar for the project.
"Well, that didn't happen."
