A pair of tough blows for the NFC West-leading Niners (8-2-1) as they prepare for a road game at St. Louis on Sunday three weeks after a 24-24 tie with the Rams on Nov. 11 at Candlestick Park.
"That was a major hit," running back Anthony Dixon said Tuesday. "Kyle and Kendall are both go-to guys in our offence. They made a lot of plays for us this year, and to see them go down on one play -- man, that's crazy. We pride ourselves on being a stacked team, on being deep, and we've just got to show up this week."
An announcement on who will start Sunday at quarterback is expected from coach Jim Harbaugh on Wednesday. Colin Kaepernick has won the last two games in his first two career NFL starts, while Alex Smith is now fully healthy from a concussion sustained in the first half of the last meeting with the Rams.
"We've got two good quarterbacks. Whatever way coach decides to go, we're behind him," Gore said. "They're both going to play well. It don't matter."
Hunter was the second player in two days to be lost for the year after Williams said Monday his 2012 season had ended.
"Two players that help our team," Gore said of the losses. "At the running back position, we've got depth. I respect Tony's (Dixon) game a lot. He makes big plays. I know coach (Tom) Rathman, whoever he's got next on the depth chart, they'll get him ready to play."
The 49ers said Tuesday both players had been placed on season-ending injured reserve. Williams announced Monday on Twitter that he tore the anterior cruciate ligament in his left knee, while Hunter is listed out with an ankle injury -- though some of his teammates said he was undergoing treatment on his left Achilles tendon in the training room.
Hunter, a fourth-round draft pick in 2011 out of Oklahoma State, had 72 carries for 371 yards and two touchdowns this season in an increased role as the team's second-leading rusher behind Gore.
Hunter and Williams were hurt on the second-to-last play of the third quarter of Sunday's 31-21 win, on which Hunter ran for a 2-yard gain. The players were helped off the field and then carted to the locker room. Harbaugh said Monday that Williams was injured before contact when his foot planted into the turf.
The 24-year-old Williams -- a third-year pro who had two costly fumbles in a 20-17 overtime loss to the Giants in last season's NFC championship game -- had 14 catches for 212 yards and a touchdown this year.
Now, James will probably get his first true look on the field. The rookie out of Oregon rushed out of the locker room to a meeting before addressing reporters.
"I expect dynamic plays, man," Dixon said. "I watch him every day on the practice field, and he's making plays, going up to get the ball. They have him doing Percy Harvin stuff when we're playing teams like that, and he really is a great talent. I feel like he's going to come in and make plays. I know he's hungry."
San Francisco activated running back Jewel Hampton from the non-football injury list and added him to the 53-man roster. They still have one open spot on the active roster and worked out kickers on Tuesday morning.