Williams has revealed a software issue that affected both of its cars during qualifying for the Belgian Grand Prix was the reason for its disappointing Q3 performance.

Valtteri Bottas gets away in eighth place with Felipe Massa in tenth after being hampered by the glitch throughout the session, though the team believes this won't affect them in the race.

Either way, Williams will start behind both Force Indias, putting them on the back foot in their brewing tussle over fourth in the constructors' standings.

"We had the problem throughout qualifying. It was a software issue, of which we're still trying to find more details. First of all we need to find out if we can fix it for tomorrow or not, because some of the numbers are still blocked and the team is still finding out what, within the regulations, we can do. Because of the problem we couldn't run the best engine mode and that cost us maybe about 0.3s today.

"Our race pace was looking very promising but, of course, we need to see how it goes tomorrow. If the temperatures will become cooler that will help us."

Indeed, Bottas believes the issues stems from Mercedes rather than a Williams one.

"Williams people don't type in the numbers on the software. I think the problem is from the Mercedes side but only in our team."