McKinnon (knee) is expected to be placed on injured reserve and may have to undergo surgery, Ian Rapoport of NFL Network reports.
General manager John Lynch said Wednesday that McKinnon had suffered a setback during practice Tuesday, and it now looks like surgery may be on tap for the running back. His season is not officially over, as Rapoport reports that the 49ers are still open to McKinnon returning eventually, but the tailback is now slated to miss a significant amount of time. Tevin Coleman and Matt Breida are now the clear top options in San Francisco's backfield to open the season.