Head coach Unai Emery said after that match that the club is likely to sell a couple of players this week as they look to trim the squad.
West Ham have registered their interest in Perez, who has a £5million valuation.
West Ham director of football Mario Husillos added: "He is a very experienced player that Manuel and I both know well from Spain".
Alfredo Pedulla claims the Florence outfit are keen on signing the 22-year-old on loan with an option to purchase, with West Ham considering cashing in as Fernandes has fallen down the pecking order following the recent acquisitions.More news: Indonesia natural disaster death toll jumps to 347
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He has Premier League experience having spent a two-year spell at Aston Villa, leaving in 2016.
Since making that move a permanent one, Sanchez has only made nine appearances for Fiorentina and was loaned out to Espanyol as he struggled for a first-team spot in Florence. After spending six years there, he would sign for Spanish team Elche but he only lasted a year at that side before signing for Aston Villa.
West Ham are closing in on the signature of versatile Arsenal forward Lucas Perez but he may not be the only Spaniard arriving from north London on Deadline Day, as the Hammers are considering a late move for Tottenham's Fernando Llorente.
The forward now looks set to complete a move to West Ham in the coming days. He left for Fiorentina on loan after that relegation and made that move permanent past year.