SANTA CLARA (AP) — Brandon Jacobs balanced himself on crutches walking through the San Francisco 49ers locker room. LaMichael James strolled through with a backpack and a smile.

What at first looked like at least one — if not two — long-term injuries for San Francisco’s newest running backs in Saturday’s 20-9 preseason loss at the Houston Texans on Saturday suddenly doesn’t seem so bad.

“I’m doing all right,” Jacobs said as he walked by reporters. “Can’t complain.”

Neither can anybody else on San Francisco’s side.

Coach Jim Harbaugh said Monday that Jacobs’ left knee could be healthy enough for him to start the regular-season opener for San Francisco (No. 4 in the AP Pro32) at Green Bay (No. 1) on Sept. 9. James, the team’s second-round pick out of Oregon, said he is ready to practice already after injuring his left ankle and riding a cart off the field in the fourth quarter at Houston.

Texans cornerback Kareem Jackson barreled helmet-first into Jacobs’ knee for a tackle in the first quarter Saturday. The big, burly Jacobs — a two-time Super Bowl winner with the New York Giants — rolled over, his knee bent awkwardly, and he lay on the ground for more than a minute until Harbaugh helped him limp off the field.

While Jacobs hobbled around slowly at the 49ers’ sunny Silicon Valley headquarters, that’s about the best he and the team could have hoped for given what was first feared.

“Brandon for the opener is possible,” Harbaugh said. “Again, we just have to see how the treatment goes, how the body responds.”

Now 30 years old, Jacobs ran for 571 yards and seven touchdowns last season as a backup to Ahmad Bradshaw. He is the fourth-leading rusher in Giants history with 4,849 yards, but saw his role diminish with the emergence of Bradshaw.

The 6-foot-4 Jacobs — who lost about 15 pounds to meet his offseason goal of dropping to about 260 — had been counted on to take over in short-yardage situations. All four of his rushes in the preseason opener against Minnesota led to a 49ers first down, and by all accounts he had been ready to lighten the load on three-time Pro Bowler Frank Gore.

“Brandon is good,” Gore said. “I’m happy that it wasn’t that serious. He’ll be back in a week or two. He’ll be fine.”

James already is back to work.

He also declined to talk to reporters at length — typical for injured 49ers players — but said he could practice again if needed. James’ left ankle remained planted when 49ers tackle Derek Hall fell on him while the running back was blocking in the fourth quarter. He was carted off the field.

James, the 61st overall pick in this year’s NFL draft, rushed for 5,082 yards and 53 touchdowns on 771 career carries in three seasons with the Ducks, who beat Stanford in Harbaugh’s final year with the Cardinal in 2010 and again last season to capture the Pac-12 title.

He joined Gore, Jacobs, Kendall Hunter and Rock Cartwright as part of a retooled running back group for the reigning NFC West champions this offseason and is also an electric returner.

San Francisco plays at Denver on Sunday for its third of four preseason games.

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NOTES: OLB Aldon Smith practiced for the first time since he injured his hip in the 17-6 victory against Minnesota in the preseason opener on Aug. 10. Smith, who had a franchise-rookie record 14 sacks and finished runner-up for the AP NFL Defensive Rookie of the Year award, moved fast and furiously and showed no signs of lingering effects during the portion of practice open to reporters. ... TE Delanie Walker also returned to practice. He injured his right knee injury during practice on Aug. 12 and hadn’t participated since. ... James was in uniform and watched practice on the field but wasn’t in pads.