SANTA CLARA, Calif. --San Francisco 49ersrunning backCarlos Hydeon Friday was ruled out of this weekend's game at the St. Louis Ramswith a stress fracturein his left foot.
Hyde, the NFL's ninth-leading rusher with 470 yards, did not practice this week after saying he suffered the injury at the New York Giants on Oct. 11.
Coach Jim Tomsula intimated earlier in the day that the starting running back's availability would be determined closer to game time.
Playing on the Rams' artificial turf in the Edward Jones Dome might have worsened the injury, which needs rest and/or surgery to heal.
"All that stuff's looked into," Tomsula said. "I'm not in that debate and don't necessarily have an opinion on whether that affects you different or not. ... I don't know that we ever play on the exact same turf anywhere. It's like grass; you don't play on the same grass, either."
Reggie Bush, whose strained left calf suffered in the season opener and aggravated at the Giants seems to be fully healed, is expected to start at running back.
The Niners' offense, which is ranked 32nd in the NFL and has scored the fewest points in the league, might be weakened further with leading pass-catcher Anquan Boldin, who has 31 catches for 372 yards and two touchdowns, listed as questionable after his hamstring tightened up on him in practice Thursday.
"We're going to make sure we're on the safe side with that," Tomsula said.
If Boldin can't go, Jerome Simpson, who recently served a six-game suspension, could make his regular-season Niners debut. The 49ers also have undrafted rookie DeAndrew White.
49ers RB Carlos Hyde (foot) won't play vs. Rams