The San Francisco 49ers fear starting running back Jerick McKinnon suffered a season-ending knee injury on Saturday.
Head coach Kyle Shanahan told reporters during a conference call that McKinnon suffered the injury making a cut "on air".
"No one was around him," Shanahan said. "He just went down. It looked awkward. We're concerned about it, but we don't have an MRI done so we don't know for sure.
"We're nervous about it, that’s for sure. We hope that we're wrong.
"It was unusual — the timing of it. A couple of hours before final cuts and we are extremely concerned. But we won't know for sure until we get an MRI.
"So he's got to be a part of our 53 [man roster] and if we get a bad MRI, then obviously he'll have to go on IR [injured reserve]. So that's why everything is very fluid. It affects our 53, our practice squad, everything."
San Francisco signed McKinnon to a four-year, $36.9 million deal this offseason.
McKinnon rushed for 570 yards and three touchdowns while hauling in 51 passes for 421 yards and two touchdowns for the Minnesota Vikings last season.