Celtic currently have a full line up (11 players) out injured with Tierney withdrawing from international duty. Bad luck or a growing trend?
The current injury list would be a decent (albeit a bit defensive) staring XI:
Gordon
Gamboa
Tierney
Simunovic
Ajer
Brown
Ntcham
Kouassi
Bitton
Arzani
Griffiths
Having all your recognised defensive midfielders out at the same time is becoming a common pattern at Celtic. In recent times all strikers have been unavailable and the run of centre back injuries all together.
But is the problem a growing one? Here is the overall injury data for the last four seasons:

I have included all first team regulars in the players counted. Rodgers benefitted from only 12% unavailability across the first treble season, and the invincibility of the team domestically may not have been a coincidence.
Since then the injury situation has been getting worse. This season is seeing an average of 17% of players injured at any given time. Assuming a squad of 25 players, this equates to 4 players being out at any point.
What could be the cause of this? It could just be bad luck, but other contributory factors could include:
Earlier season starts due to Champions League qualification = less rest
Cumulative impact of increasing numbers of games (getting to 6 domestic finals, Europa League Group Stage, more European qualifiers)
More matches on artificial pitches
More intense method of playing under Rodgers – more pressing
Poor scouting (Compper had a bad injury history for example)
There may be many other reasons to do with training methods and conditioning work undertaken at the club.
In terms of the current squad, which players have missed the most games?

Boyata’s recent form and emergence into the Belgian team has not been helped by regular injury at Celtic.
Simunovic has missed 32% of all Celtic’s matches over the last four seasons.
Hayes has not really established himself at the club not helped with a long absence due to a broken leg.
Griffiths seems to suffer from regular but no prolonged injury absences, especially with calf issues.
Rogic’s absences amount to 18% of all matches which may not be as high as people think.
Similarly, Forrest has missed only 3% of all matches over the last 4 seasons surely putting to bed the injury prone label.
And as I pointed out on Twitter, there is but one player who has been available for all 203 matches over this period – Callum McGregor.