Ange Postecoglou has revealed Mikey Johnston and Karamoko Dembele are set for an extended spell on the sidelines.
The Celtic duo both limped out of last week's friendly against Bristol City and the manager admits they face a "fairly significant" rehab period.
He could not put an exact timeframe on their return but indicated it will be over a month before either player will get back on the pitch.
Postecoglou has signed Liel Abada and will rely on James Forrest but remains short of attacking options in wide areas, with new addition Kyogo Furuhashi facing a wait before he can join the Celtic squad.
And now he will be forced to make do without Dembele and Johnstone for a period of time.
Postecoglou said: “We’ve had some early diagnosis, but they have both had fairly significant injuries and will be out for a period of time.
They are the kind of players I love having in the team.
“We don’t want to put a time frame on it but it won’t be less than a month. How much longer? We are waiting for advice.
“It’s disappointing for both of them.
"I was looking forward to working with them as they are exciting wingers, the kind of players I love having in the team.
“Unfortunately, that game at Bristol has really cost us, through no one’s fault. One was a bad tackle, and the other an innocuous event.
“It’s a blow and they have some fairly significant rehab ahead of them.
"They have youth and time on their side so hopefully they will work hard and get back.”
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