Having qualified a strong 10th, the F1 rookie reported a loss of power on his STR10 during the formation lap and was called into the pits before the race start. The team quickly identified and fixed the issue - a loose connector in the engine - and sent Sainz back out, though he now was two laps down.
With 11 laps to go, Toro Rosso elected to retire the Renault-powered car in order to save engine mileage.
“We decided to continue the race because in Spa you never know what can happen,” said Tost. “Maybe a Safety Car or some rain could’ve helped us, but unfortunately this never happened.
“I’d like to apologise to Carlos for this, as it’s now the fourth race in a row where he can’t finish a race because of technical problems.”
Indeed, Sainz “ran out of power all of a sudden” in Austria before his car “switched off” while running P9 at Silverstone. At Budapest, it was a broken hose clip that denied the reigning Formula Renault 3.5 Series champion another opportunity to add more points to his 2015 tally.
Sainz’ series of technical gremlins means he is yet to score since finishing 10th at last May’s Monaco Grand Prix. The 20-year-old currently sits 16th in the Drivers’ standings with nine points.
Click here for Sunday's gallery of the Belgian Grand Prix at Spa-Francorchamps.