Lattimore (knee) has informed the 49ers that he plans to retire, the team's official site reports. Serious knee issues derailed the 2013 fourth-rounder's career, with Lattimore relaying in a statement Wednesday that getting his knee "fully back to the level the NFL demands has proven to be insurmountable," the San Jose Mercury News reports. With Lattimore no longer a candidate to join the 49ers' backfield, Frank Gore and Carlos Hyde remain the team's top two options at the running back position.