The 18-year-old's current contract runs out in 12 months but he has made a decision to move elsewhere after not accepting the reported five million euros ($5.58 million) per season contract offered by AC Milan, the club announced on Thursday.
AC Milan, who have recently been boosted by a major new investment, have been linked with Ronaldo after his surprise revelation.
Not only would that rule Real Madrid out of the race to sign Donnarumma - who has made it clear he wants to leave the club - it would also leave United in need of a goalkeeper.
The 18-year-old goalkeeper told Milan last week he did not wish to renew his contract, which runs until the summer of 2018, opening up the prospect of a possible transfer this summer.
But his stay at the San Siro looks to be coming to an end after the club met with Donnarumma's agent Mino Raiola for crunch talks on Thursday.
"For the moment, nothing will happen". Everyone was quite tense in the first half and we didn't get into the final third the way we usually do.
"We made him an enormous offer considering his age and the burden it would place on Milan".
"Right now, we are not after Donnarumma".
"We wanted to make him a symbol of Milan for our fans and Gigio had everything required to fill that role", he added.
However, Madrid seemed to cool their interest in De Gea due to the good form and dressing room backing of Keylor Navas, but the prospect of getting him as part of a swap deal could appeal. We both simply took stock of the situation and went our separate ways.