Blick newspaper reports that, early on the final day of the rare in-season test, "acrid black smoke" emanated from Sauber's upgraded C31 car at the Italian circuit.
"The smoke was so strong it could be smelt in the media centre," wrote veteran correspondent Roger Benoit.
"Sergio Perez had to have his eyes treated with drops because of the fumes."
The Mexican driver admitted: "It was very unpleasant."
Blick said the cause of the smoke was a burned plastic cover.
Perez went on to complete 118 laps on Thursday.