The US space agency is preparing to download all useful data remaining in Opportunity's flash memory to earth and switch the rover to an operating mode that does not use flash memory.
Flash memory retains data even when power is off. Individual cells within a flash memory can wear out from repeated use. Reformatting clears the memory while identifying bad cells and flagging them to be avoided, media reports said.
Opportunity has been active for more than a decade and is currently about 200 million km from earth.
"The flash reformatting is a low-risk process, as critical sequences and flight software are stored elsewhere in other non-volatile memory on the rover," said project manager John Callas from Nasa's Jet Propulsion Laboratory in Pasadena, California.
Nasa sent rovers Spirit and Opportunity to Mars in early 2004.
Spirit worked for six years while Opportunity is still active, sending data about ancient wet environments on Mars.