Williams driver Felipe Massa says tyre debris from Formula 1 rival Lewis Hamilton's punctured Mercedes was to blame for his disappointing run to 13th in the Belgian Grand Prix.
Massa started ninth, but collected debris from the controversial collision between title protagonists Hamilton and Nico Rosberg at Les Combes on the second lap of the race.
The Brazilian says this robbed his FW36 of downforce, which cost him the chance to challenge for points while team-mate Valtteri Bottas raced to a fourth podium in five races.
"On lap two or three of the race I picked up tyre debris from Lewis and it was stuck in the floor of my car," Massa explained.
"I was complaining in the first stint that something was wrong because the car was impossible to drive.
"I could feel I was missing a lot of downforce. I was maybe two seconds slower every lap.
"They didn't remove it at the first pitstop, so I did another 12 laps doing the same - two seconds off every lap - so for half the race I lost maybe 30s or more compared to what I was supposed to be doing.
"I was still complaining the whole stint and at the second pitstop they saw the tyre and removed it, and I was two seconds quicker every lap.
"It was really a shame. It was really tough because it was possible to fight for points today."
Williams's performance chief Rob Smedley expressed disappointment at failing to get both cars home in the points on a weekend where his team was expected to challenge the works Mercedes cars.
"What happened with Felipe today was just extremely unlucky," Smedley said.
"I'm disappointed we missed out on a boat-load of points with Felipe, but you can't mitigate for a big bit of debris going under the car.
"It was a huge piece of tyre from Lewis' car that got stuck under the car for half the race, which we could only just about get out at the second stop."