SAN FRANCISCO — Jim Harbaugh declined Monday to "rehash" the 49ers' decision to play Aldon Smith on Sunday, and the coach instead discussed how they'll forge ahead without their sack leader, who is on indefinite leave for treatment after his recent drunken-driving arrest.

"There's adversity. There's an opportunity to stare it in the face and whip it," Harbaugh said.

Smith reportedly was flying to a rehabilitation center Monday morning, according to ProFootballTalk.com. Harbaugh declined confirmation and said an official statement will be forthcoming, presumably from the 49ers or the league.

Smith is expected to bewas placed on a non-football-injury list. His timetable of returning is unknown, as is his destination for treatment.

The 49ers likely will use a committee of defenders to fill in for Smith, who played all 72 defensive snaps in their 27-7 loss to the Indianapolis Colts.

Smith was a part-time player in 2011, so look for defensive coordinator Vic Fangio to again shuffle players into that spot at right outside linebacker and right defensive end, depending on if it's a run or pass situation.

Three players stand out as likely temps in place of Smith.

-- Demarcus Dobbs: A third-year veteran, Dobbs is their top backup on the defensive front. Suspended for the opener because of his own alcohol- and marijuana-involved car accident, he's rotated in the past two games, typically spelling defensive tackles Justin Smith and Ray McDonald. He has no career sacks in 26 games.

-- Corey Lemonier: The rookie, third-round pick out of Auburn likely would be used strictly as a pass rusher. He hasn't had any snaps on defense, but 24 on special teams. He had two sacks in the exhibition season.

-- Dan Skuta: Base defense likely is where Skuta will be deployed. After four years with the Bengals, Skuta looked solid in the exhibition season and had three sacks. But he hasn't taken a defensive snap through three regular-season games (46 special-teams snaps).

Another option is Tony Jerod-Eddie, but he's listed as the only backup at nose tackle behind Glenn Dorsey, who became the starter after Ian Williams' season-ending ankle injury Sept. 15 at Seattle.

Drafted in the first round in 2011 out of Missouri, Smith did not add Sunday to his total of 37 career sacks.

Smith apologized after the game for his actions and said he would "fix" his "problem."

"We're supportive of Aldon, as we are of all players, all of our coaches, our personnel. Always supportive of in-house," Harbaugh said. "We've hashed through it and now taken steps, and Aldon's taken steps."

Linebacker Patrick Willis (groin) and cornerback Nnamdi Asomugha (right knee) were having MRI exams done on their injuries Monday, Harbaugh said.

Wide receiver Jon Baldwin could debut Thursday in St. Louis after what Harbaugh called "very good" practices last week. Baldwin was acquired in an August trade with the Kansas City Chiefs in exchange for A.J. Jenkins.

Rather than chastise his receiving corps for its recent lack of production, Harbaugh said the entire offense's "precision needs to be better."

Perhaps epitomizing the lack of receiving depth Sunday, the 49ers trailed 13-7 when they lined up these five wideouts for a second-and-10 play: Anquan Boldin, two backup tight ends (Vance McDonald, Garret Celek), a backup running back (Kendall Hunter) and their fullback (Bruce Miller). Kaepernick ended up completing a 4-yard pass to Hunter to the 49ers' 45-yard line. Kaepernick got sacked on the next play for a 7-yard loss and the 49ers then punted with 11:14 remaining.

Harbaugh said he remains "very confident" in quarterback Colin Kaepernick.

Frank Gore had no physical ailment that prevented him from having more than three carries after a strong first half, Harbaugh said.

Asked why Gore didn't get more carries, Harbaugh replied: "Those were the plays that were called."

The 49ers (1-2) are in their first two-game losing streak since Harbaugh became coach in 2011.

"Football's not easy," Harbaugh said. "There are struggles. That's one of the things you enjoy about the game. We've got some adversity, there's no question about it."