The attacking midfielder was something of a bit-part player for the Blues last season, making only 28 starts in all competitions.
Sky Italia (via Football Italia) (opens in new tab) reported on Friday that Ziyech had handed in a transfer request at Stamford Bridge.
And, according to the Guardian (opens in new tab), Chelsea have made the 29-year-old available transfer.
Ziyech is thought to be open to joining Milan - who won their first Serie A title in 11 years last season - but a deal might not be all that straightforward, with his wage demands potentially proving problematic.
The Dutch-born Morocco international only arrived at Chelsea from Ajax (opens in new tab) two years ago, in a move worth an initial £34 million.
But he has struggled for consistency with the Blues and, in turn, lately, a regular starting berth.
His cause has hardly been helped by Thomas Tuchel's switch to a front two, leaving room in the side for an advanced playmaker - a capacity in which Mason Mount was imperious last term.
A move to Milan would appear to suit both parties, with the Rossoneri said to be seeking competition for Brahim Diaz - their main man in the number 10 role.
Ziyech could be one of two Chelsea players heading to Serie A this transfer window, with Romelu Lukaku set to return on loan to Milan's arch-rivals Inter (opens in new tab).
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Tom Hancock started freelancing for FourFourTwo in April 2019 and has also written for The Analyst and When Saturday Comes, among others. He supports Wycombe Wanderers and has a soft spot for Wealdstone. A self-confessed statto, he has been known to watch football with a spreadsheet (or several) open...
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