The Sauber-run squad is sixth in the F1 world constructors' championship this year but has failed to score any points in the past four races, after the team picked up points in seven of the opening nine rounds.
In that run of poor results both Valtteri Bottas and Zhou Guanyu have been blighted by mechanical problems, with the Finn forced out of the British Grand Prix with a gearbox issue and the Hungarian GP with a fuel system failure, while his teammate retired from the French GP with power unit trouble.
