Monisha Kaltenborn has admitted it is not certain that Felipe Nasr will stay at Sauber beyond 2016.
Earlier, we reported that the Swiss team was likely to keep the Brazilian alongside Marcus Ericsson next year, but team boss Kaltenborn admits there have been tensions.
"Yes, we lived through times of stress," she told Brazil’s Globo.
One point of contention, Kaltenborn admitted, was recent reports that Sauber may have actively sabotaged Nasr’s car.
"Do you think we would be crazy enough to give up the fight for a better place in the championship and all the financial implications that has?" she bristled.
Kaltenborn said talks with Nasr are taking place, but one problem may be his sponsorship backing by Banco do Brasil.
"The bank’s situation is not quite the same as before," she revealed. "It’s a state enterprise and the situation is different now."
It is not believed that former Sauber driver and Haas refugee Esteban Gutierrez will return to the team in 2017, but one leading candidate may be the Mercedes-backed Pascal Wehrlein.
Kaltenborn said: "We have drivers interested in us but I would also say that Felipe is one of the drivers on our list."