Monisha Kaltenborn is confident that Ferrari will take the "next step" with their power unit as they seek to narrow the deficit to Mercedes.
Although Ferrari's first V6 engine in 2014 missed the mark, the Scuderia made great inroads last season.
Not only did the Italian outfit enter the championship with a vastly improved power unit but they also used their in-season development tokens to great effect.
Ferrari and their customers benefitted from this as the Maranello team finished runner-up in the championship while Sauber went from scoring no points in 2014 to amassing 36 a year later.
"I am confident, they [Ferrari] have already shown in 2015 the step they took," Sauber team boss Kaltenborn told Motorsport.com.
"You can't expect miracles, the gap [to Mercedes] is so big that you have to take it step-by-step, and you also have to look at the reliability.
"But I think they have done a very good job, and I have all reasons to have no doubts, or rather to have the belief that they are going to take the next step."
But while confident that Ferrari's 2016 engine will be a step forward, Kaltenborn concedes that catching Mercedes may be a leap too far.
"I think the teams which had the Mercedes engines in the first year, when this engine [formula] came in could have a bigger benefit then you could have now," she said.
"Because simply the other teams were so far back, and that's already closer. So yes, there can be a benefit, but definitely a smaller one than that time, because the differences are no longer so big.
"If Ferrari were to make that kind of step where they are couple of seconds away from the rest, then you could compare it to that, but that kind of advantage we are not going to have."