Lecavalier, who signed a five-year, $22.5 million contract with the Flyers in the off-season, got the diagnosis after missing three games with back spasms, Flyers General Manager Paul Holmgren said.
"He had an X-ray in Dallas and we found something on the X-ray that didn't look right," Holmgren said.
A magnetic resonance imaging exam performed Sunday in Philadelphia revealed a non-displaced fracture in Lecavalier's lower back.
"We're going to treat it when we can as aggressively as we have to right now," the GM added. "We told him to rest for a few days to get some of the discomfort out and we'll go from there."
Lecavalier leads the Flyers with nine goals in 22 games this season.