The 31-year-old has not played for the Scottish champions since beating Morton 5-0 in the Scottish Cup.
He was conspicuously absent from the bench during Parkhead’s League Cup final victory over Rangers.
And now Ange Postecoglou has explained the situation of the Scotland international.
He said: “James Forrest suffered a slight muscle strain in training so he will be out for a while which is unfortunate for him.
“He will likely miss the next period beyond the international break.”
The Australian also provided an injury update for the rest of the squad.
He revealed everyone came through the weekend’s 5-1 win against St Mirren in good shape.
“Everyone else has been fine since the weekend but I will rate everyone who played on Sunday,” he continued.
“It’s three games in six days so we’re definitely going to make some changes, whether it’s Wednesday or Saturday I’ll see how the squad is.”
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Meanwhile, Hearts boss Robbie Neilson has said he wants to ‘spoil’ Postecoglou in his 100th game as Celtic manager.
The two sides meet at Parkhead during the next round of Scottish Premiership games as the Jambos look for their first win at the venue in over 14 years.
In the previous two meetings this season, the Hoops won 2-0 and 4-3 and Neilson has claimed he is keen to avoid a repeat of those results in the forthcoming clash.
Ahead of the game, he said: “Ange did a fantastic job, there’s no doubt about that. He has instilled in the team a way of playing and a style of play that is entertaining.
“He has done exceptionally well. But hopefully we can go there and spoil this celebration.
“You have to be solid in defense. But you also have to believe that if you have the ball you can hurt them.”
“If you watch teams that have some success there, then they control phases of the game, they choose the right pass at the right time and the right movement.
“We have to do that. The atmosphere there is always electric and it’s a difficult place, but it’s one that gives us a chance to challenge ourselves as coaches and also as players.”
https://www.heraldscotland.com/sport/23369401.ange-postecoglou-provides-james-forrest-celtic-injury-update/?ref=rss Ange Postecoglou provides update on James Forrest Celtic’s injuries