Club Brugges boss Carl Hoefkens said Charles De Ketelaere is struggling mentally amid constant Milan links.
Recent report suggest a deal for the Belgium international to join the Rossoneri is close and there have even been suggestions he could be in Milan by the weekend.
De Ketelaere did not train with Brugges in recent days and Hoefkens said it was because the player was worried about suffering an injury ahead of his potential move.
Hoefkens said: “As coach, I want everyone on the pitch capable of giving 100% at every moment.
“If someone says they cannot do everything physically, tactically or mentally, it is my job to tackle the issue.
“He [De Ketelaere] said it was becoming too heavy mentally and that he was worried about injuring himself in training so there is only one conclusion: stop training with the group.”
Asked if he was disappointed by De Ketelaere, Hoefkens added: “No, I have known Charles a long time and I have been heavily involved in his growth.
“At times it happens that there are other thoughts, I try to focus on the players who are present 100%.”
Milan directors Paolo Maldini and Ricky Massara recently held two separate meetings with their Brugge counterparts and reports suggested that on both occasions, despite the two clubs being close to an agreement, they were unable to strike a deal.
Premier League duo Leeds United and Everton were also reportedly interest in the player.
However he is allegedly willing to take a salary cut in order to force through a move to Milan.