UEFA confirmed in late June they had taken drastic action against Milan's apparent breaches of break-even requirements, barring them from competing in Europe's second-tier competition for next season.
Milan, who qualified for the Europa League by virtue of finishing sixth in Serie A, immediately launched an appeal to CAS.
And their ban from the competition has, as a result, been annulled, although they could still end up with some form of punishment, with CAS telling UEFA to "issue a proportionate disciplinary measure".
UEFA's initial sanction related to Milan's failure to fulfil the break-even requirement set out in the governing body's Financial Fair Play regulations.
While CAS accepted this decision, rejecting the Rossoneri's request to force UEFA into a settlement agreement, it claimed the ban from Europe was not a proportionate punishment.
CAS also said UEFA's Adjudicatory Chamber had not properly assessed some "important elements" and pointed to the takeover of the club's holding company by Elliott Management this month as a sign of Milan's improved financial situation.
A CAS statement read: "The CAS panel rejected AC Milan's request to order UEFA to enter into a settlement agreement but acknowledged that the decision of the adjudicatory chamber of the UEFA Club Financial Control Body (CFCB) to exclude AC Milan from the UEFA club competition was not proportionate.
"The Panel considered that some important elements have not been properly assessed by the adjudicatory chamber, or could not be properly assessed at the moment when the appealed decision was rendered, and noted in particular that the current financial situation of the club was now better, following the recent change in the club's ownership.
"The panel decided to refer the case back to the adjudicatory chamber of the UEFA CFCB because the club had requested that the case be referred back to UEFA and because it considers that the adjudicatory chamber is in a better position than the CAS panel to issue a new proportionate disciplinary measure on the basis of the current financial situation of the club."
And UEFA have confirmed that Milan will now be reinstated for the upcoming season.
"Earlier this month, the Adjudicatory Chamber of the independent Club Financial Control body, chaired by José Narciso da Cunha Rodrigues, decided that AC Milan had breached the UEFA Club Licensing and Financial Fair Play Regulations; in particular the break-even requirement," read a statement. "As a result, the Chamber decided to exclude AC Milan from the 2018/19 UEFA Europa League.
"As is permitted by Article 34(2) of the Procedural rules governing the UEFA Club Financial Control Body, as well as Articles 62 and 63 of the UEFA Statutes, AC Milan appealed this decision to the Court of Arbitration for Sport, who confirmed the Chamber’s view that there had been a breach of the regulations.
"However, the CAS noted that there were some important elements that could not properly be assessed by the Adjudicatory Chamber – most significantly the improvement of the Club’s financial situation as a result of the recent change of ownership.
"As a result, AC Milan is reinstated to the 2018/19 UEFA Europa League and the CAS has referred the case back to the Adjudicatory Chamber to decide on the appropriate disciplinary measure, in the light of these developments."