Lazio has released the following statement on their website: "Isaksen player will immediately begin a rehabilitation program following the protocol established by the *Biancocelesti* medical staff, to enable his return to competitive action within the scheduled timeframe".
Isaksen also withdrew from the Danish national team camp in May, where Denmark was scheduled to play friendly matches against DR Congo and Ukraine.
Lazio has appointed a new head coach since the end of last season; Maurizio Sarri has been replaced by Gennaro Gattuso.
Isaksen is under contract with Lazio until the summer of 2028. The 24-year-old Dane has played 95 matches in Serie A so far.