Jim Harbaugh was absent from the 49ers practice Thursday under doctor's orders, instead heading for the Stanford Hospital to undergo what the team described as a minor procedure for an irregular heartbeat.
Harbaugh was feeling abnormal Wednesday night and was seen by team doctors at Stanford, where the procedure was advised.
The second-year head coach is expected to be back at practice on Friday.
Assistant head coach and special teams coordinator Brad Seely will be overseeing Thursday's practice and meetings.
Players were made aware of Harbaugh's condition at the end of the Thursday morning walk-through when Seely addressed the team on the field.
"Like he always tells us, he's tougher than a two-dollar steak," Patrick Willis said. "So we know he's going to be alright. We have a bunch of great coaches here that will keep everyone on track. So we're going to practice as if he was here."
"The first thing you think is, 'How serious is this?'" punter Andy Lee said. "They said it wasn't serious and it shouldn't be a big deal. I'm sure everything will be fine and he'll be back tomorrow."
"He's a strong person and he'll overcome it," safety Dashon Goldson said. "Our prayers are with him and his family, and we'll see him tomorrow"
Harbaugh was scheduled for an 11:45 a.m. press conference, but it was public relations director Bob Lange who appeared at the podium to announce the news.
We will update this story as more information becomes available.