Guerendo (foot) was listed as a non-participant on Monday's estimated injury report, Nick Wagoner of ESPN.com reports.
Guerendo's first career start Sunday against the Bears was fruitful until he exited in the fourth quarter due to a foot injury. Prior to his departure, he notched 128 yards from scrimmage and two rushing TDs on 17 touches. Coach Kyle Shanahan revealed the nature of the injury Monday, calling it a sprain and the running back day-to-day, per Nick Wagoner of ESPN.com. Shanahan also told Lindsey Pallares of the 49ers' official site that the team will "evaluate him over the next few days and see if he's got a shot" to play Thursday against the Rams. If Guerendo ultimately isn't able to go Week 15, he'll pass off the backfield to Patrick Taylor, while Israel Abanikanda (inactive Week 14) and practice-squad member Ke'Shawn Vaughn (two carries for four yards Sunday) will be the reserve options.