Leigh Griffiths will miss Celtic's crucial Champions League qualifier against Midtjylland on Wednesday with a "slight injury", says Ange Postecoglou.
Celtic will take a 1-1 draw from the home leg into their game against Danish club Midtjylland as they bid to progress from their Champions League second qualifying round tie.
And they must attempt to do so without Griffiths, although his fellow striker Albian Ajeti has recovered from the issue which forced him to miss Saturday's 6-2 friendly defeat by West Ham.
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On Griffiths, Postecoglou said: "He picked up a slight injury yesterday (Monday) in training, which was disappointing for him because he was obviously going to be part of the travelling party.
"Albie trained yesterday and he is fine, so he will be involved. Everyone else from the weekend, apart from Leigh, pulled up fine."
Griffiths was booed by a section of fans during Saturday's friendly defeat by West Ham following recent police and club investigations into his social media activity.
Police Scotland said it had established "no criminality" after carrying out a "full assessment" of claims that the 30-year-old striker had exchanged improper messages with a 15-year-old girl as well as another teen girl, and he returned to the fold for Celtic last week.
Postecoglou said: "In terms of the crowd response, Leigh is in the same position as all of us. We represent the football club and the supporters are there to judge us on how we perform and what we do. We have to accept any response we get from them.
"For the most part, Leigh still got a positive response from the crowd because they acknowledge the fact that he has had a very good career at Celtic and has contributed.
"If there are people who express dissatisfaction, it's up to him to show with his performances and the way he goes about things. I am sure he can win them back very quickly."
Celtic travelled to Denmark with an inexperienced back-line following Nir Bitton's first-leg red card.
But new signing Carl Starfelt is set to be available for Saturday's Premiership opener against Hearts, with the Sweden centre-back in quarantine in London following his move from Rubin Kazan.
Postecoglou, who added that Christopher Jullien faced another "couple of months" out as he battles back from a knee injury, said: "Carl has started some individual training and we are hoping he joins us at Lennoxtown by the time we get back to Scotland.
"We will see what his condition is like then but he should be available by the weekend."
New Celtic boss Postecoglou admits he has been left frustrated by delays in the club's recruitment policy due to coronavirus.
The Australian joined the club this summer with the task of wrestling the Scottish Premiership title back from the hands of Old Firm rivals Rangers.
But with the new campaign kicking off this weekend, progress in the transfer market has hampered the new man's plans to rebuild the squad.
Speaking exclusively to Sky Sports News, Postecoglou said: "It's probably the one area we're chipping away but not having the visible results.
"Of course we've signed Liel Abada who came in and had a fantastic debut as well as Carl Starfelt and Kyogo Furuhashi but both of them are not here right now which are the challenges of the world we live in at the moment.
"That's the frustrating bit - it would have been great to have those two boys in already and the other ones we are working on concluded a bit quicker.
"That's not through a lack of wanting or hard work - we're endeavouring to get there and chipping away and hopefully over the next two or three weeks we'll bear the fruit of that."