Sauber propped up the constructors' standings last year, scoring just five points to nearest rival McLaren's 30 as it struggled with a year-old Ferrari power unit.

Having switched to a current-spec engine, the team was once again slowest in the 2018 season opener in Melbourne – but the C37 blossomed into a midfield regular and an occasional Q3 threat as the campaign wore on.

Asked by Motorsport.com for his take on Sauber's recent progress, Szafnauer said: “I don’t know how they had such a steep development curve.

“I think they outdeveloped the top teams this year from last year. From where they ended last year to where they are now, they outdeveloped everybody.

“I don’t know how that happens with a small team, but we’re got to figure that out, because they’re smart guys.”

Sauber's progress has convinced former F1 champion Kimi Raikkonen to return to the team on a two-year deal after losing his Ferrari seat, with the Finn joined by Ferrari protege Antonio Giovinazzi in 2019.

The Swiss outfit sits eighth in the teams' standings with two races left, and will record its best points tally for the season since 2013 should it score a top-10 finish in Brazil or Abu Dhabi.

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Szafnauer reckoned Sauber's 2019 campaign could “maybe” suffer if the team over-committed resources to the in-season development of the C37.

“I don’t know when they stopped developing this year’s car, because we stopped quite a long time ago to focus on next year,” he said.

“If they continued developing this year’s car in areas that don’t translate to next year, then it can hurt them.

“If it translates, if what you learned this year works next year too, than it doesn’t hurt. They can apply it.

“But I am impressed with their development rate, very, very impressive.”

Team boss Frederic Vasseur has previously claimed that Sauber was to cease 2018 development at the end of July.