The England captain was cited after making contact with Jack Clement's head with his shoulder in Saturday's (AEDT) Premiership match between Saracens and Gloucester.
Farrell believed the incident did not merit a red card, prompting a disciplinary hearing on Wednesday (AEDT).
A four-match ban was upheld, however, potentially ruling Farrell out until after Sarries' clash with Leicester Tigers on 20 February. England plays both Scotland and Italy before that date.
But the final match of the suspension will be removed if Farrell completes the World Rugby Coaching Intervention Programme, which he has indicated he intends to.
An initial six-match ban was reduced after Farrell acknowledged the charge and showed "exemplary" behaviour during the hearing process.
It could not be reduced further at the outset due to a previous five-match suspension in 2020 for a high tackle on Wasps' Charlie Atkinson.