The Italians are keen to strengthen their squad, following the departures of a number of first-team players, and have set their sights on the Premier League pair.
Their interest in Santon has been longstanding, with the San Siro side keen to bring him back to Italy following a successful period at St James’ Park.
It is unclear as to whether the player himself is looking to move on, but he could be tempted by the prospect of Champions League football.
Santon was on the books at Milan’s local rivals Inter before switching to the Magpies, but this has not deterred them from considering a move.
They are also believed to be monitoring the situation of goalkeeper Krul, with the Dutchman viewed as a candidate to be the club’s long-term number one.
The 24-year-old is under contract until 2017, but Milan are confident that they can lure him away.
However, they are unlikely to move for the stopper until the summer.
Meanwhile, manager Alan Pardew is set to ask wantaway defender Fabricio Coloccini to remain at the club until at least this summer.
The Argentine is keen to return to his homeland for personal reasons, and has reportedly asked the club to release him from his contract.