The club confirmed the timeframe of the injury in a statement released on Monday, after the teenager underwent surgery earlier in the day.
Now a report in El Mundo Deportivo has estimated that the 18-year-old is set to miss a whopping 30 matches for the club, but could be available to return in time for theoretical Champions League quarter-finals and a Copa del Rey showpiece.
The period of time would cover a period of 17 league matches, starting with the trip to Atletico Madrid later this week and concluding with the trip to Osasuna in early March.
The teen would also sit out every round of the Copa del Rey apart from the final, while he will also miss the remainder of the Champions League group stage and the Round of 16.
Fati is now one of the established attacking players at the club along with Lionel Messi and is aiming to establish himself ahead of the likes of Antoine Griezmann, Ousmane Dembele and Francisco Trincao.
The teenage prodigy has also starred for Spain in recent times – netting one goal in four international appearances having earned his first cap in September, while he has netted five goals in 10 games for his club this campaign.