SANTA CLARA, Calif. _ Running back Jerick McKinnon sustained a season-ending knee injury in practice Saturday, ruining what had been a promising and pricey addition to the 49ers offense.
McKinnon tore the anterior cruciate ligament in his right knee the first day back in team drills since straining his right calf Aug. 9.
"It was the last play of practice, made a cut on air, no one was around him, just went down, looked awkward," coach Kyle Shanahan said in a media conference call.
Shanahan was "extremely concerned" it could be an ACL tear before tests confirmed that diagnosis three hours later.
Shanahan also noted the "unusual" timing of McKinnon's injury, in that it came a couple hours before the 49ers' roster got pared to the 53-man limit prior to the deadline. The media had no previous notice or access to Saturday's practice.
Shanahan said a "bad MRI" would lead to the 49ers placing McKinnon on injured reserve as he faces reconstructive surgery and about a year of rehabilitation.
Among those cut Saturday were running back Jeremy McNichols and Jeff Wilson. On Friday, the 49ers released running back Joe Williams, a 2017 fourth-round draft pick who sustained a rib fracture two weeks ago.
"We're concerned but we're also confident," general manager John Lynch said. "We've got a lot of good football players here and we're proud of our 53-man roster. Next week we're going to be really excited looking to take on the Vikings."
In the wake of McKinnon's calf strain and Matt Breida's Aug. 9 shoulder separation, the 49ers signed veteran Alfred Morris two weeks ago, reuniting Morris with Shanahan from their Washington days in 2012-13. The only other running back on the current roster is Raheem Mostert, who's more of a special-teams ace.
Shanahahn said Breida returned to practice Saturday, as did tight end George Kittle, who also sustained a shoulder separation in the exhibition opener.
The 49ers signed McKinnon, a former Minnesota Vikings backup, to a whopping four-year, $30 million deal as free agency opened in March. He started the Aug. 9 exhibition against the Dallas Cowboys and was held to minus-4 yards on three carries while also making a 7-yard catch.
