AC Milan have been referred to UEFA's Adjudicatory Chamber over alleged breaches of Financial Fair Flay regulations.
The Italian giants have been monitored in relation to potential infringements for several months and had an application for a voluntary agreement to restructure their finances rejected by UEFA's Club Financial Control Body in December.
Milan invested more than €200 million (£175m/$236m) in their playing squad following the takeover by Chinese investors Rossoneri Sport Investment Lux last year and their ability to repay a loan by October is central to UEFA's concerns.
If Milan are eventually penalised over the breaches, exclusion from the Europa League could be an option at the governing body's disposal.