United signed the Brazilian for £52m last summer but he has struggled to make an impact in the Premier League.
Fred has yet to make an appearance for Ole Gunnar Solskjaer's side in 2019/20 and has not even been included in a matchday squad so far this season.
Fiorentina are considering making an offer before the European transfer window closes next Monday.
However, United are reportedly holding out for at least £27.3m, which could prove to be a stumbling block.
Fiorentina hope that the Red Devils will lower their asking price before September 2.
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