Nikola Kalinic has reportedly attracted interest from Eintracht Frankfurt, but Milan are demanding €35m for the striker.
According to Calciomercato.com, Schalke and Frankfurt were both approached by intermediaries representing Kalinic in January.
Although Schalke rejected their advances, the website notes Frankfurt did show an interest.
However, Milan would only be prepared to sell the Croatian for a profit, having agreed to pay Fiorentina €25m for an obligatory purchase option last summer.
The 30-year-old has scored just four goals for the Rossoneri this season, with injury problems limiting his impact.
However, CM notes he has shown “physical improvements” in recent training sessions and could be given a chance to impress against Roma on Sunday.
Frankfurt, for their part, beat RB Leipzig 2-1 on Monday to move up to third in the Bundesliga table.