HOUSTON -- Brandon Jacobs and LaMichael James, two key additions to the 49ers' running back stable, were carted off Reliant Stadium's field Saturday night with leg injuries.
Neither injury -- to Jacobs' left knee and James' left ankle -- is of the season-ending variety, coach Jim Harbaugh said with relief after the 20-9 exhibition loss to the host Texans.
Jacobs' injury is the more serious, as his knee collided with cornerback Kareem Jackson's helmet at the end of an 8-yard, first-quarter run.
"He's going to miss a little time," Harbaugh said of Jacobs. "The ACL is good. The patella is good. It'll be some time, but we'll see."
ESPN reported that Jacobs, the 49ers' newfound short-yardage specialist, will undergo an MRI exam Sunday.
James went down with just over four minutes remaining. Harbaugh said "things look good" on an X-ray, and James echoed that optimism by vowing not to miss any practice time come Monday.
"It just twisted out of place," James said. "When it happened, I was like, 'No!' I kind of tweaked it the first preseason game (Aug. 10), so it's kind of recurring."
Quarterback Alex Smith termed it a "scary" sight seeing those injuries take out the newest members of a well-stocked running back corps.
"You hate seeing it in preseason," Smith said. "Luckily, it looks like good news."
Smith barely escaped injury himself in two series of work, getting sacked twice and later hit high on a play that drew a roughing-the-passer penalty.
Smith said most of his punishment was "self-inflicted" as he tried to flee a crumbling pocket. But Harbaugh cited the offensive line's missed assignments, and left tackle Joe Staley agreed with that contention.
Jacobs found a nice hole to burst through on his only carry. Then came every running back's nightmare: a helmet hitting his knee.
Jacobs couldn't put weight on his leg as he hopped to the sideline with the assistance of Harbaugh and lead trainer Jeff Ferguson. A cart then took Jacobs to the locker room for further evaluation.
Acquired in the offseason after winning his second Super Bowl with the New York Giants, Jacobs excelled in his 49ers debut in the exhibition opener against Minnesota. All four of his carries that game resulted in first downs on short-yardage, "and-1" situations.
Jacobs' absence became magnified at the end of Saturday's second series, when Anthony Dixon was stopped for no gain on fourth-and-1 at the Texans' 20-yard line. Dixon, to his credit, did convert a fourth-and-1 run five snaps earlier.
There was a bright side for the suddenly beleaguered running back corps: Frank Gore made his exhibition-season debut and delivered a 14-yard run on his first carry.
"I feel real good," said Gore, who was stopped for minus-2 yards on his only other carry, which immediately followed Jacobs' exit.
Harbaugh said of Gore: "He looks as spry as ever. We're right on track with Frank."
Another offensive highlight: Randy Moss made his first receptions in a 49ers uniform, although Michael Crabtree and Mario Manningham got the starting nods. Moss had three catches for 24 yards, and he nearly had a fourth reception, but it bounced off his outstretched hands at the Texans' 5-yard line.
Harbaugh said there was no concerted effort to throw that often to Moss, who declined to comment in the locker room.
Colin Kapernick (4 of 8, 19 yards) said the one throw he wanted back would have gone to an open Moss. Instead, Kaepernick threw to Ted Ginn Jr. on the other side of the field, and it nearly got intercepted.
Harbaugh rated Kaepernick's outing as "pretty darn good." On his second snap in relief of Smith, Kaepernick scampered for a 12-yard gain, a play similar to his 78-yard touchdown run in the exhibition opener against Minnesota.
All four of the 49ers' quarterbacks saw action. Smith completed 5 of 9 passes for 49 yards, highlighted by a 24-yard reception to Ginn on a third-and-5 play.
Josh Johnson entered in the third quarter, and his first pass resulted in a 32-yard, over-the-shoulder catch by rookie A.J. Jenkins. Johnson (4 of 6, 64 yards) took a shot at the end zone on the next play but overthrew an open Jenkins.
Scott Tolzien was 4 of 9 for 23 yards in fourth-quarter work.