Westbrooks was given credit for time served during his sentencing on Friday, and he's expected to attend the start of Rams voluntary offseason workouts Monday.
Westbrooks, 27, was arrested on suspicion of carrying a loaded firearm and four other charges after a traffic stop on Interstate 5 outside Bakersfield in September. Prosecutors later formally charged Westbrooks one count of carrying a loaded firearm.
The four-year veteran has played in 71 games with the Rams since signing with the team as an undrafted free agent in 2014.
Westbrooks faces the possibility of discipline from the NFL under the league's personal conduct policy.