49ers shutting McKinnon down until Week 1

The San Francisco 49ers won't take any chances with their big-money free-agent acquisition.

After starting running back Jerick McKinnon avoided a major knee injury last week in practice, only suffering a calf strain, the 49ers will keep him on the sidelines until Week 1, general manager John Lynch told Brian Murphy of KNBR 680 on Friday.

McKinnon is set to be the focal point of head coach Kyle Shanahan's much-lauded rushing attack after signing a four-year, $30-million deal.

The 26-year-old had nearly 1,000 yards from scrimmage and five touchdowns for the Minnesota Vikings last season.

Backup running back Matt Breida is also sidelined with a shoulder injury, which necessitated the signing of free agent Alfred Morris as additional depth, so the 49ers are being understandably cautious by shutting down their top back for the remainder of the preseason.