McKillop, who led the team in special teams tackle last year with 31 and was expected to be one of the first linebackers off the bench this season, suffered a torn ACL and a torn patellar tendon in his left knee during Wednesday's afternoon practice and is likely out for the season. An MRI on Thursday revealed the injury.
McKillop, a second-year player from Pittsburgh, is one of several injured 49ers: guard David Baas, tight end Delanie Walker and linebacker Travis LaBoy are nursing mild concussions; center Eric Heitmann is suffering from a shoulder stinger; and offensive lineman Chris Patrick has a sprained shoulder. None practiced, although guard Chilo Rachal was back on the field after missing a day because of dehydration.
The Niners called an audible and changed their practice location from their team headquarters in Santa Clara, Calif., to Cal State University Monterey Bay on the central California coast. Temperatures are typically much cooler along the coast, and coach Mike Singletary said it was done as a change of pace.
"I planned this a while ago," he said, "and felt that if we went forward, this would be a good way, a good time, to do it. I just feel it gives the guys a change of pace, and the rest of the day we're going to just continue to do some of the things we need to do in order to get better."
Although temperatures have not been especially hot in Santa Clara, the Monterey coastline was clearly a milder change. It was 53 degrees when players got off the team bus in the morning, and it never got above 61. Coaches wore jackets throughout the practice, which lasted from 10:25 a.m. until 12:50 p.m.
Singletary didn't schedule an afternoon workout, but he hinted he might have something special in store for his players.
"I can't tell you that one," he said. "But we're just going to finish off the day and it will be good."