Brendan Rodgers has confirmed Celtic will be without Cameron Carter-Vickers and Maik Nawrocki for around two months.
It means the injured duo - along with Stephen Welsh - will miss the match against St Johnston on Saturday and the trip to face Rangers at Ibrox on September 3.
Carter-Vickers was forced off in the win over Aberdeen with Nawrocki also picking up a hamstring knock in the Viaplay Cup loss to Kilmarnock.
Welsh has had an operation after his injury setback he suffered in Celtic training hours after signing a new deal at Parkhead.
Confirming the injuries, Rodgers said: It's obviously disappointing in terms of Cameron Carter-Vickers and Maik Nawrocki. Stephen Welsh probably about eight weeks.
"He had an operation just the other day, he has come through that well.
"The other two we were hopeful that they would be back sooner but further scans on them puts them at probably about eight weeks."
He added: "Reo Hatate will be back at the international break, round about that. Mikey Johnston will be next week.
"Yuki Kobayashi will be at the international break and Oh will return to training next week.
"Alistair Johnston is back and has trained well and will be available for the weekend."
It leaves Brendan Rodgers with just new signing Gustfa Lagerbielke and Liam Scales as the recognised first-team centre-backs in the squad from now.
However, Rodgers confirmed Celtic will look to sign another defender - with an emphasis on landing an "experienced" centre-back to ease the defensive injury crisis.
He said: "I think we have to look at it, there is no doubt it is an area we are light on.
"When you are losing three players for that length of time and knowing the number of games that we will have and the importance of every game, it's definitely something we have to look at.
"I think especially at centra-half it's a specialised position where the experience always helps.
"We've got lots of young players in the squad but naturally to bring those players on and bring them through they need to play with players not just of experience, but players of quality.
"You need to hopefully try and align both because you'll see the best of those players, the guys that are young and developing and dealing with the expectation - they can play alongside the guys that's going to pull them through and bring out that potential, ideally that's what you want.
"That's something that we will look at."
