ST. LOUIS >> San Francisco 49ers running back Reggie Bush has been carted off the field with a knee injury after slipping on concrete near the stands on a punt return and will not return.

Bush was making his first start of the season in place of the injured Carlos Hyde. The 49ers ruled him out at the start of the second half.

Bush entered Sunday’s game against the St. Louis Rams with just eight carries for 28 yards and a long gain of 9 yards.

Hyde was ruled out earlier in the week with a foot injury. He was ninth in the NFL with 470 yards rushing with a 4.1-yard average and three touchdowns.

Bush made his first start since Dec. 28, 2014, for Detroit against Green Bay. His last 100-yard game was Nov. 28, 2013, when he had 117 yards against Green Bay.

Browns quarterback Josh McCown slipped on concrete further downfield last week and rammed into the padded wall in front of the stands, and walked away shaking his left arm. McCown stayed in the game.

49ers tight end Garrett Celek (concussion), safety L.J. McCray (knee) and running back Mike Davis (hand) also have been ruled out at the start of the second half and cornerback Keith Reaser (ankle) is questionable to return.