Depleted Celtic are facing an injury crisis unlike anything they've seen in recent times.
But none of their many absences have been felt quite as heavily as that of Callum McGregor.
The 28-year-old has stepped into Scott Brown's shoes and has been a rare beacon of consistency in a topsy-turvy start to Ange Postecoglou 's tenure.
But he hasn't been seen since he left the pitch against Ross County and it's no coincidence the Hoops have dropped off without him.
The Premier Sports Cup win over Raith is their only victory in the four games he has missed with no combination of James McCarthy, David Turnbull, Tom Rogic and Ismaila Soro quite finding the magic formula.
So it comes as a relief to Postecoglou to have McGregor back in his thinking ahead of the Europa League crunch tie with Bayer Leverkusen.
As he gets set for a potential return, then, Record Sport have taken a look back at Celtic's recent record with and without their No.42 - to assess just how much of an impact his comeback could have.
Celtic with Callum McGregor
If there's one thing that will define McGregor's career, it's just how consistently available he is.
Whether it's for club or country, it takes something major to keep him out.
To get a fair reflection on McGregor's impact on the Celtic team, you have to go back to the beginning of the 2019/20 season - the last time they won the league.
Incredibly, he's started 110 out of their last 121 matches in all competitions - including 12 of their 16 this season as his importance shows no signs of waning under Ange Postecoglou.
He failed to miss a single league game in 2019/20 while he missed just two the season after as the relentless amount of football he'd played began to take its toll.
Their ten defeats with him on the pitch last campaign, however, took its toll on their title credentials as the Hoops yielded the Premiership crown to Rangers.
Celtic with Callum McGregor since 2019/20: W75 D18 L17
Win percentage: 68%
Celtic without Callum McGregor
To get a fair reflection on McGregor's impact on the Celtic team, you have to go back to the beginning of the 2019/20 season - the last time they won the league.
That season was abridged by the coronavirus pandemic but it remains remarkable that he only failed to start three times all season.
Two of those were European dead rubbers against Cluj and Kalju - the other was a Scottish Cup tie with Clyde.
In the time since, he has only sat out eight games, with Celtic winning three and losing four of those - most recently drawing with Dundee United with him on the sidelines.
Their win rate when he isn't on the pitch, however, drops by as much as 23 per cent.
Celtic without Callum McGregor since 2019/20: W5 D1 L5
Win percentage: 45%
