The 49ers could be without running back Matt Breida against the Green Bay Packers next Monday.

That's because the second-year pro sustained a "mid- to high-ankle sprain," a source told NBC Sports Bay Area's Matt Maiocco.

Breida left Sunday's 28-18 loss to the Arizona Cardinals on Sunday, but a source told Maiocco that the X-rays came back negative. Breida rushed for 56 yards on eight carries, and he caught a 5-yard touchdown pass on the game's opening drive. 

The 23-year-old ended Sunday as the NFL's fifth-leading rusher, and his 7.5 yards per carry are the highest among running backs with a minimum of 15 carries. 

Breida took over as the 49ers' lead running back after Jerick McKinnon tore his ACL in the preseason. Alfred Morris and Raheem Mostert are the healthy running backs on the roster, while rookie Jeff Wilson is on the team's practice squad.