The San Francisco 49ers opened training camp with a crowded backfield, but those options have dwindled rapidly.

The team's running back depth chart took another hit during Sunday's season-opening win over the Tampa Bay Buccaneers when free-agent acquisition Tevin Coleman went down with what head coach Kyle Shanahan confirmed Monday as a high ankle sprain, ESPN's Adam Schefter reports.

Shanahan said Coleman will likely miss the team's Week 2 matchup Sunday against the Cincinnati Bengals, but added that he'll be week-to-week afterward, according to the San Jose Mercury's Cam Inman. The 49ers coach also downplayed the possibility of the tailback ending up on injured reserve.

In Week 1, the fifth-year veteran contributed six carries for 23 yards on the ground and two catches for another 33 yards through the air. Fellow running backs Matt Breida and Raheem Mostert handled backfield snaps in Coleman's absence against Tampa Bay.