Everton and Milan were in talks over a deal for Deulofeu as the winger hasn't featured for the Toffees as much as he would have liked this season.
The former Barcelona youngster has made just four starts in the Premier League in the current campaign and has failed to feature in Koeman's side's last five games.
The 22-year-old was widely expected to join AC Milan on loan in order to gain some much needed minutes, but the deal has now been put in doubt.
Everton want AC Milan to pay a loan fee, something which the Serie A side are not happy to do.