The Serbia international missed Saturday's 2-1 win over Aston Villa with a hamstring injury but has otherwise been a regular starter for Forest since his 2024 move from Fiorentina, racking up close to 100 appearances for the club.
Milenkovic is admired by Milan boss Ruben Amorim, according to Calciomercato, with the Serie A side said to be evaluating the 28-year-old as a possible option to strengthen their defensive ranks in January.
Inacio remains top of Amorim's mid-season wish list, but the Portuguese defender carries a €40 million price tag. Milenkovic, who is under contract until 2029, is viewed as a "more affordable" alternative amid a reported €28 million valuation.
Whether Nottingham Forest would even consider selling in the new year is another matter, with central defence an area they may look to strengthen rather than weaken when the window reopens, rather than letting one of their defenders leave.
Head coach Oliver Glasner already has limited natural centre-back numbers following the deadline-day departures of Morato and Zach Abbott on loan, a shortage exposed at Villa Park when both Milenkovic and Jair Cunha were ruled out through injury on the eve of the match.
Full-back Ola Aina switched into the right-sided spot in Glasner's back-three system as a result, while Ousmane Diomande made his first Premier League start in the middle position usually occupied by Milenkovic.
Glasner has since ruled Milenkovic out of Forest's next fixture against Coventry City, with the defender expected to be available when the Reds return from the international break away at Crystal Palace.
AC Milan have already raided Forest's squad once this summer, agreeing a loan with an option to buy for winger Omari Hutchinson before the transfer window closed, a deal in which Amorim was also said to be heavily involved.
Milenkovic, who came through the ranks at Partizan Belgrade before establishing himself in Serie A with Fiorentina, remains a key figure in Forest's defensive plans and has become a reliable performer since his switch to the Premier League in 2024.