Gomez was forced off in the 1-1 draw against Cagliari with what was found to be medial collateral ligament damage following a clash with goalkeeper Michael Agazzi.
Fiorentina have confirmed that the former Bayern Munich striker is likely to miss at least six weeks of action.
"The striker will wear a brace for two weeks before beginning a rehabilitation programme to bring him back up to match fitness gradually," the Serie A club said in a statement.
"The recovery period is expected to last six to seven weeks."
Gomez was signed by Vincenzo Montella in the close-season, with the Germany international having scored twice in the league so far this campaign.
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