Frederic Vasseur has admitted that the departure from Sauber of technical boss Jorg Zander was "awkward".
The Swiss team announced suddenly at the end of last week that just 18 months after re-joining Sauber and Formula 1, Zander has left.
Blick reports that the departure comes after several personal incidents involving the German, who worked in F1 for BMW, Williams, Honda and Brawn.
It is believed that the incidents involved alcohol.
"We had to part in a rather awkward situation," team boss Vasseur said.
"But now we have to look forward, as we are already starting to develop the car for 2019. We must also prepare for the race in Barcelona, so let's see how we perform there."
Sauber are ninth in the constructors' standings heading in this weekend's grand prix.
