United States international Antonee Robinson revealed a dream move to Milan broke down because his medical revealed a heart problem.
The left-back looked set to leave English second-tier side Wigan Athletic when Milan made its move on deadline day in January.
However, the 22-year-old saw his hopes of a San Siro switch dashed when a health issue became apparent during routine checks.
Robinson has not played in the six weeks since that transfer collapsed, and has now disclosed he will undergo a procedure in an effort to control his heart rhythm.
"During my medical for a potential transfer to Milan on deadline day, an irregularity was picked up in my heart rhythm," Robinson said, in a statement released by Wigan.
"Further testing was required to ensure the move could be finalised and ratified, though there was not enough time to complete this before the transfer deadline."
Robinson said he has "undergone a period of testing and treatment" and despite feeling "absolutely fine", he acknowledges the issue must be dealt with before he can return to playing matches.
He added: "Following consultation with the club's medical staff and independent specialists, it has been decided I will need a medical procedure later this month to address the irregularity in my heart rhythm - a procedure called an ablation."