San Francisco 49ers coach Jim Harbaugh was sent to the hospital Thursday for a "minor procedure" after doctors discovered he had an irregular heartbeat.

The team said it anticipates Harbaugh will be back at the 49ers facility Friday, though it's unclear in what capacity. No details about the procedure were given.

The NFC West-leading 49ers (6-2-1) host the NFC-North leading Chicago Bears (7-2) on Monday night at Candlestick Park.

"It's one of those things that, like Coach Harbaugh always tells us, he's tougher than a $2 steak," 49ers linebacker Patrick Willis said. "We know he's going to be alright. We know we have a bunch of great coaches here that keep everything on track, and we're going to practice today as if he was here."

Team spokesman Bob Lange said no incident had occurred at the facility. Instead, Harbaugh had visited with doctors Wednesday night after feeling ill, and they advised him to have the procedure done at Stanford Hospital.

Players were informed of Harbaugh's hospitalization by assistant head coach and special teams coordinator Brad Seely during Thursday morning's walkthrough. Seely also oversaw team meetings and the afternoon practice.

Players said the news caught them by surprise.

"He was pretty good. We were slapping hands and talking yesterday," 49ers safety Dashon Goldson said of Harbaugh. "I didn't see anything. He showed no emotions. He didn't show anything like that."

Added Willis: "He seemed fine to me. He actually sat right behind me in meetings," Willis said. "He seemed fine. I didn't know anything was wrong. But like I said, we know he's going to be alright."

Suddenly, quarterback Alex Smith's recovery from a concussion is San Francisco's second-biggest injury concern.

The 48-year-old Harbaugh won NFL Coach of the Year in his first season with the 49ers after coming over from Stanford, where he had engineered a Cardinal resurgence. The always intense coach's impact was immediately felt up the road in San Francisco.

Harbaugh led San Francisco to a 13-3 record in the regular season and back to the playoffs for the first time since the 2001-02 season. The 49ers lost in overtime to the New York Giants in the NFC championship game.

Harbaugh and his wife, Sarah, welcomed their first son Sept. 4 — and Harbaugh didn't even have to miss a full practice, just an afternoon walk-through. Jack Jr., named after Harbaugh's father, was the couple's third child, joining two big sisters, Addison and Katherine.

San Francisco scout team safety Michael Thomas starred at Stanford under Harbaugh and has known the coach since Thomas was a 17-year-old recruit from Houston. He said he has seen Harbaugh — whom he calls a mentor and friend — exhaust himself for years but never imagined his health could be in jeopardy.

Thomas sent Harbaugh a text to wish him well — and not to hurry back until he's healthy.

"In his mind, he's serious, like I never get sick, I never take a day off, blah, blah, blah," Thomas said. "To actually see something like this happen to a man who's so passionate about his job and about this team, to see him be taken away, you wish him well but you know it's just killing him not being here."