The 29-year-old hasn’t kicked a ball since September 19 and has missed matches for both club and country.
Celtic manager Neil Lennon has confirmed that Forrest went under the knife on Tuesday and now faces a recovery period of between six and eight weeks, potentially ruling him out until 2021.
Forrest had scored twice and registered one assist in his seven Premiership games prior to his injury but now doesn’t look likely to play again until the new year.
Lennon had better news on defender Christopher Jullien who has been nursing a back injury.
He last featured for the Bhoys in the 5-0 win at Ross County on September 12 but should return to action after the international break giving him a chance of involvement against Hibs at Easter Road and in the travelling party for the return match against Sparta Prague.
Long-term absentee Mikey Johnston has also returned to training.
Lennon said: “Mikey Johnston has been training but he’ll be a while yet. Christopher Jullien will resume training soon, hopefully he’ll be back in contention after the international break.
"James Forrest had surgery this week so will miss a considerable time.”
The Celtic boss also confirmed that the club’s latest round of coronavirus testing had produced no cause for concern; a stark difference from Thursday night's Europa League opponents Sparta Prague, who haven’t had their troubles to seek with the virus.
Lennon continued: “We’ve had our own issues so we do have sympathy for Sparta. Our latest tests from yesterday have all returned negative.”