Niners 'nervous' after Jerick McKinnon injures knee

An offseason hampered by injuries struck again for the San Francisco 49ers.

Starting running back Jerick McKinnon suffered what appears to be a concerning injury on Saturday, NFL Network Insider Ian Rapoport and NFL Network's Mike Garafolo reported.

"He made a cut on air. It was the last play of practice," coach Kyle Shanahan told reporters. "He made a cut on air, no one was around him. He just went down. It looked awkward. We're concerned about it but we don't have an MRI, so we're not sure. So, he's going to get that done right now. But something with the knee. We'll find out later. We're nervous about it, for sure.

"Today was the first day we allowed him to practice with the guys. On the day of the game he was out there running routes, doing stuff with the other guys not dressing with the quarterbacks, and things like that. He's been running routes and doing things but today was his first day back in live drills, or 11-on-11 drills."

McKinnon will undergo an MRI.

Depending on the severity of the injury, it could be a big blow to the 49ers' offense. McKinnon was expected to play a large role in his first season under Shanahan. McKinnon is the type of dual-threat pass-catching back with between-the-tackles ability that thrives in Shanahan's system.

Alas, injuries have already curtailed his availability. The 26-year-old was just coming back from a muscle strain in his calf. Now an apparently new injury struck.

The 49ers' backfield is also dealing with an injury to Matt Breida (shoulder). With McKinnon's injury coming so close to the start of the regular season, unless it was a minor scare, we'd expect him to miss time.

The injuries, along with the releases of RBs Jeremy McNichols, Jeff Wilson Jr. and Joe Williams, put veteran Alfred Morris on track to play a big role early in the season.

UPDATE: An MRI revealed McKinnon suffered a torn ACL and will miss the 2018 season, Rapoport reported.