Ange Postecoglou admits it will be a challenge to fill the void left by Callum McGregor as the “influential” Celtic captain prepares for a lengthy period on the sidelines.

The Hoops are still waiting to learn the exact extent of the knee injury that forced the Scotland midfielder off in Wednesday’s 3-1 Champions League defeat by RB Leipzig in Germany.

However, manager Postecoglou did confirm on Friday that “it’s not a short-term one”.

“There’s a reason Callum is the captain,” he said. “He’s a fantastic player who contributes to the way we play our football. He is influential on and off the field so you can’t just replace him with one person overnight.

“That just doesn’t happen. It’s about other people filling in the breach. We missed him for a few games last season, it’s just something we have to cope with.

“I’m disappointed for Callum more than anything because he’s very influential and he wants to be involved all the time. His performances have been super but we just have to deal with what’s ahead of us.

“The one thing I know about Callum is whatever timeline they give him, he’ll try and come back earlier. That’s what happened last year with his cheek fracture. He got the mask on and played.

“He’s been around long enough to know this is part of being a professional footballer. You’re not always going to play 70 games a year. Injuries will happen. He’s just been unlucky the other night. He’s a professional on and off the field and he’ll tackle his rehab as determined as anyone.”

Postecoglou plans to make “at least two or three changes” to his team for Saturday’s lunchtime trip to St Johnstone as Celtic bid to ease their Champions League disappointment in midweek by remaining ahead of city rivals Rangers at the top of the cinch Premiership.

Liel Abada is back in contention, while Aaron Mooy and Cameron Carter-Vickers also have a chance of returning following injury.

“The early kick-off on Saturday makes it more challenging because hours of recovery are important,” said the Hoops boss. “We didn’t get in until 2am on Thursday so we’ve only really got a 48-hour turnaround to get guys ready for another game. Every hour counts.

“It’s where we’re at and what we’ve got to deal with. We’ll make at least two or three changes because we know it’s going to be a challenging game and we need to freshen up the team. We’ve got some guys who have been training well and we’ll put them in the team and give them an opportunity.”