Bush was injured after running off the field and slipping on the concrete surrounding the field in a Week 8 loss to the St. Louis Rams. Edward Jones Dome, the Rams home stadium, is owned and operated by the city of St. Louis through its Sports Authority and Convention Bureau.
According to the report, the running back will likely seek gross negligence in the lawsuit. The 49ers placed Bush on injured reserve and he will be out for the remainder of the season.
The NFLPA reportedly contacted the NFL about the safety issue at the stadium following the latest incident on the concrete.
Bush, 30, signed a one-year deal with San Francisco in March and dealt with a calf injury earlier this season. In 2014, Bush ran for 297 yards and two touchdowns with 253 receiving yards in 11 games with the Detroit Lions.