Celtic defender Carl Starfelt will be out until after this month's international break with a hamstring injury.
The Sweden international limped off midway through the second half of the goalless draw against Livingston in the Scottish Premiership at Parkhead on Saturday.
Starfelt, a summer signing from Rubin Kazan, will miss the Europa League game against Ferencvaros on Thursday and the league match at Dundee on Sunday, live on Sky Sports.
"We lost Carl Starfelt in the last game and similar sort of timeline to Tommy (Rogic) I suppose, we are hoping he will be back after the international break, but he will definitely miss these two games," Celtic manager Postecoglou said.
"It is always a blow when you lose players to injury. To be fair to Carl, he has played every game since he got here and it's not surprising that he has something like this happen.
"We would have loved to have rotated him earlier, but we tried to build some cohesion, consistency in the back four and we didn't want to chop and change too much because we had to at the start of the season."
Celtic, who are on a six-game unbeaten run in all competitions, will turn to 21-year-old centre-back Stephen Welsh or experienced Israel international Nir Bitton in the absence of Starfelt.
Postecoglou added: "We have options. Welshy has been raring to go and has been unfortunate not to get an opportunity to play, because whenever he has played he has been very good for us and Nir can slip back there as well so there are options."
Celtic sealed their first points of the Europa League campaign with a 2-0 win over Hungarian champions Ferencvaros in their previous game in October.
Kucbcksuyz
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speed recovery
Kucbcksuyz
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we have backups