The Colombian defender is down the pecking order in Italy and may fancy a move to England.
The Blues are currently short on centre-halves, with Stones and Phil Jagielka the only two senior defenders currently in their squad, with Sylvain Distin and Antonlin Alcaraz both having left this summer.
Stones has been the subject of intense speculation during the current transfer window, with Premier League champions Chelsea already seeing several bids rejected for his services - as reported by Sky Sports.
Zapata move makes sense regardless of Stones outcome
Even if Stones doesn’t leave this summer, Zapata may still be of interest to Everton given their current lack of numbers in defence.
Given that he is in the final year of his contract, the Italians could be keen on a deal so as to avoid losing him on a free next summer, and the presumably low price for his services would be of great interest to the Toffees.
At 28 years old he is far from over the hill either, while his defensive experience would be something Martinez would likely be keen to add to his squad given the loss of Distin at the end of his contract.
He would likely be keen on a move to England as well having slipped down the pecking order at Milan, with the likes of Alex, Philippe Mexes and Gabriel Paletta all ahead of him in Italy.