San Francisco 49ers running back Reggie Bush is believed to have a torn ACL, and will likely miss the rest of the 2015 season, according NFL reporter Ian Rapoport.

Bush slipped on concrete after running out of bounds on a short pick up against the St. Louis Rams. Bush needed assistance from trainers, and from the video, the injury looked immediately significant, via Dieter Kurtenbach of KNBR.

The 49ers running back suffered a calf strain in week one against the Minnesota Vikings, and has struggled to make an impact since signing with San Francisco this offseason. The 49ers' starting running back Carlos Hyde was ruled out this week with a foot injury, and the team waived running back Jarryd Hayne this weekend.

With Bush out the 49ers will likely try to bring Hayne back, as they've been decimated at the running back position. Bush had only rushed for 28 yards this season before suffering the season-ending injury, and has struggled to stay healthy throughout his NFL career.

The former first-round pick by the Saints in 2006 has only completed a full 16-game season twice in his NFL career. Bush only signed a one-year contract with San Francisco prior to this season, and as an unrestricted free agent next year it is unclear where he will end up. Bush can be a dynamic player on the field, but has struggled to stay healthy in his 10-year NFL career.