The former England midfielder has been a free agent since his contract at Goodison Park expired in June but continued to work hard under manager Sean Dyche to try and find his way back into the side this season.
Cesc Fabregas, head coach of Como, has said Dele could train with them, external after Christmas which could be the next big step in his career that has taken a few knocks over the years.
In a message on Instagram, Alli confirmed his departure as he looks to take on a new challenge after the Christmas break.
"Before any of that happens, it's very important for me to make clear how grateful I am to all the fans, staff and players at Everton FC for the support they have given me."
"It's been an incredibly tough journey trying to put the final pieces together to regain match fitness and I cannot thank the Everton staff enough for the hard work they have put into this process," Dele added.
"Unfortunately, things haven't worked out as we all would have hoped, and I think it's the right time for me to turn a new page. I want to wish everyone at this amazing club the very best of luck."
Alli has struggled mentally as well as physically over the last few seasons with Dyche speaking on Friday about how he wishes him well in the future.
"The major point that we agreed, as a collective, was to get him back to a good place and I think he is there.
"He's had so much misfortune with injuries, you could not imagine the challenges he has had. We wish him well and that is all we can do.
"He has been nothing but an ease for me to work with. On to a new challenge but we certainly wish him well."