Exiled Schalke midfielder Kevin-Prince Boateng will train with AC Milan until the end of 2015, paving the way for the Ghana international to return to the Serie A club permanently.
Following May's 2-0 Bundesliga defeat at Cologne, Boateng and team-mate Sidney Sam were indefinitely suspended by Schalke.
A proposed August switch to Sporting Lisbon broke down due to a disagreement over Boateng's image rights but, having previously expressed his openness to playing for a club he represented between 2010 and 2013, the 28-year-old is back in training with Milan.
He is under contract at Schalke until the end of this season so would be unable to play competitively for Milan before January if coach Sinisa Mihajlovic pursues a formal transfer.
Boateng is expected to feature in friendly and reserve-team matches during his extended trial period.
A brief statement on Milan's official website on Wednesday read: "Kevin-Prince Boateng, from tomorrow until December 31, will train with the first team at Milanello."
Ghana international Boateng is the second controversial talent to return to Milanello under Mihajlovic's watch, with Mario Balotelli currently on a season-long loan at San Siro from Liverpool.