McKinnon (calf) suffered a non-contact knee injury during Saturday's practice, eliciting concern from coach Kyle Shanahan, Nick Wagoner of ESPN.com reports. "Something with a knee, we'll find out later," Shanahan said. "We're nervous about it, that's for sure."
Shanahan's comment doesn't inspire any confidence, nor does the fact that McKinnon is already scheduled for an MRI. The obvious concern is an ACL injury, but we can't make any assumptions until McKinnon has actually been evaluated. He was working his way back from a minor calf injury, with the expectation of being ready for Week 1 in Minnesota. The Niners likely will turn to Matt Breida (shoulder) and Alfred Morris to lead their backfield if McKInnon isn't available.