The Dreamliner is nearly three years behind its original delivery date. Boeing did not say how long the latest necessary modifications would take, The Wall Street Journal reported Friday.
The company also did not say when test flights would resume.
The fire occurred at an altitude of 1,000 feet as the plane was approaching the airport at Laredo, Texas.
On board were 42 pilots, mechanics and engineers, including a Federal Aviation Administration pilot, who was at the controls when the fire erupted.
The fire did involve the plane's engines, but rather a large power panel that feeds many of the plane's electrical systems.
Some of the backup systems worked when the fire broke out, but some did not. The autothrottle system and flight-deck computer displays were among the systems that failed, the Journal said.