McKinnon suffers non-contact knee injury; ACL tear reportedly feared

San Francisco 49ers running back Jerick McKinnon suffered a non-contact knee injury during a team workout Saturday, head coach Kyle Shanahan announced, according to ESPN's Nick Wagoner.

"Something with a knee, we'll find out later," said Shanahan. "We're nervous about it, that's for sure."

The 26-year-old will undergo an MRI, added Shanahan. The fear is that he tore his ACL, a source told ESPN's Adam Schefter.

McKinnon has been out of team drills since straining his right calf Aug. 9. The 49ers opted to hold him out of the preaseason to avoid worsening the injury.

The prized free-agent signing was set to be the focal point of San Francisco's rushing attack. If McKinnon is sidelined for an extended period, Matt Breida and Alfred Morris should split the majority of the team's carries

The former suffered a shoulder injury earlier in the preseason, but is now fully healthy, Shanahan said.