The 29-year-old appeared to wave two fingers towards the away stands as he was substituted in the 68th minute of the Premier League match at St Mary's Stadium on December 30.
As a result, Austin will now miss Saturday's Premier League game at Leicester City and the FA Cup third-round replay against Derby County next week.
His absence is a further blow for Saints manager Ralph Hasenhuttl in attack, with Danny Ings and Michael Obafemi both set to miss the match against the Foxes due to hamstring injuries, while Manolo Gabbiadini has joined Sampdoria.
After the Southampton website announced the news and shared the story on their Twitter account, reaction from the Saints fanbase appeared to be mixed.
Some supporters were angry at the FA for handing out the suspension, while others pointed the finger at the player himself:
Good work @premierleague on sharply stamping down on this terrible crime against humanity. I'm sure those precious fans who were offended by the gesture will, someday God willing, recover from the brutality of @chazaustin10 's behavior. What a farce. #SaintsFC— SaintM (@SaintMikeB) January 10, 2019
Chance for Gallagher? Or new striker incoming? We need to find some urgent goals and hope Ings does not become hamstrung! ♂️♂️— Stephen Trott (@trotty1805) January 10, 2019
He wouldn’t of scored anyway..— ian hilton (@ianhilton) January 10, 2019
So no strikers for a while then, utter disaster!!— Murray Smith (@LingwoodMurray) January 10, 2019
And he only has himself to blame!— Jacko (@Jack0_P) January 10, 2019
That’s absolutely ridiculously.. shame on you @FA I would also be interested to hear what rule was apparently broken? And why they’ve decided to enforce the ban less than 48hours to a game..— Alan (@alanhenley) January 10, 2019
Austin has featured in Southampton’s last four matches in all competitions and has scored three goals for the Saints this season.