"I am going home now and we will see."
Schumacher was quoted as saying in Sport Bild newspaper: "It's possible that today was my last drive in a Formula One car."
Schumacher, younger brother of retired seven times world champion Michael, was the slowest by a considerable margin of the 20 drivers on track in Thursday's test at the Jerez circuit.
By contrast, Austrian Christian Klien was seventh fastest and Italian Giancarlo Fisichella ninth for Force India in testing on Wednesday.
A team source said the 32-year-old German suffered a hydraulics failure in the morning, spun twice and never looked comfortable in the car.
Schumacher, winner of six grands prix with Williams from 2001 to 2003, left Toyota at the end of the season in October with his future uncertain.