The teenage goalkeeper, who has been hailed as the next Gianluigi Buffon, is out of contract this time next year and now locked in talks regarding a new deal.
'It 'a final decision.
Italian media have speculated the 'keeper will be sold this summer with Raiola citing interest from Real Madrid and Paris Saint Germain.
Donnarumma, who stands at 1.96 metres, is one of the most promising young goalkeepers in Europe.
Last season Donnarumma started in all of Milan's 38 Serie A matches.
Milan are attempting to rebuild their squad after another poor league campaign saw them finish sixth in the table.
The Portuguese striker André Silva, the Ivorian midfielder Franck Kessié and defenders Ricardo Rodriguez and Mateo Musacchio have already been recruited at some cost but Milan will need to invest in a goalkeeper if Donnarumma departs this summer.
"We made a strong offer".
"We were taken by surprise, as we had hoped Donnarumma would be the goalkeeper taking Milan into the future, that we could build the team around".
"We thought we could make him one of the pillars of our project, but the player decided that his relationship with Milan will stop on 30 June 2018".