Chelsea did not include a buy-back option for Fiyako Tomori.
The Blues academy graduate joined AC Milan this summer after a successful loan at San Siro last season.
Milan paid €29 million for Tomori, who they consider “untouchable”, according to Fabrizio Romano.
The respected Italian journalist added that Chelsea did not include a buy-back option like they did in Tammy Abraham’s deal to Roma.
Tomori started for the Rossoneri in Wednesday’s loss to Liverpool in the Champions League.
The 23-year-old is considered an important player in Stefano Piolo’s side.