Raikkonen suffered from an overheating left front brake duct shortly after the start of the race at Spa-Francorchamps.
AUTOSPORT has learned that at the first pitstop, the team discovered the visor tear-off lodged in the cooling channels of the brake duct.
Although Lotus was able to remove it, the brake disc was already too hot and could not be cooled enough. Eventually it failed completely.
Investigations by the team after the race discovered no other explanation for the brake issues, which led it to believe that the visor strip was the cause.
Team principal Eric Boullier said there was no design problem with the brake cooling on the Lotus, even though it had been operating in a high temperature window.
"We know that we have two options on cooling here: one was nearly too cool, one was on the top of the range," Boullier told AUTOSPORT.
"If the failure had happened on both discs then you would think that the cooling was wrong, but it was only on one disc."