The 29-year-old has been charged by the FA with using racist language in a pre-season friendly against Mansfield Town last summer.
Despite being acquitted in March at Mansfield Magistrates Court of racially abusing Stags defender Krystian Pearce, Forestieri now faces a lengthy suspension, although if he decides to appeal the FA suspension he could yet be involved in their opening round of fixtures, and fined £25,000.
The FA statement read: “Fernando Forestieri has been given a six-match suspension and fined £25,000 after a breach of FA Rule E3(2) was found proven by a Regulatory Commission.
“It was alleged that words used by the Sheffield Wednesday player during a friendly fixture against Mansfield Town FC on 24 July 2018 breached Rule E3(1) as they were abusive and/or insulting.
“It was further alleged that the words constituted an ‘Aggravated Breach’, which is defined in Rule E3(2), as they included reference to ethnic origin and/or colour and/or race.
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“The striker has also been warned as to his future conduct and must attend face to face education but the sanction is currently set aside pending appeal.”
Forestieri has already served a three-match ban for misconduct relating to that incident. He was also fined £25,000.
Argentina-born forward Forestieri is not the first footballer to face FA proceedings after being acquitted in a court of law.
Former England captain John Terry was cleared in July 2012 Westminster Magistrates’ Court of racially abusing Anton Ferdinand during a clash between Chelsea and Queens Park Rangers.