Let's be clear, losing 7-1 to PSG isn't a crime. PSG are a magnificent team with a thunderously lethal front-line which contains the world's second best player.
But the fact that Celtic weren't able to even slow them down, and ended up taking their second 7-1 loss in two seasons (getting thumped 7-1 by Barcelona last season) despite taking a shock lead inside of a minute does not bode well for the future of the side under Rodgers' direction.
Consider that this Celtic side are incredibly dominant on the home front. They last lost a domestic game at the tail end of the 2015/16 league title, when they were already Champions. Since then they have played 64 times and not suffered a defeat.
Yes, that means what you think. They went through the entire 2016/17 season without losing once in the league, despite getting thumped 7-1 at the Camp Nou. So far this season they're unbeaten at home but have lost four games, all in Europe.
The aggregate score in those games? 21-5. And alright the Astana result (4-3) was conditioned by winning the first leg 5-0, but still, this all points to a very disturbing trend. Despite being overwhelmingly dominant at home, Celtic are simply not up to the standard required in the Champions League.
Celtic are nowhere near qualifying for the knockout rounds (and who knows the horrors that would await them once they got there). That is the next step they have to take in order to improve. A Europa League run would be nice, but the end goal has to be progression in the biggest club competition in the world.
And how can they reach that level? They receive little-to-no challenge on the domestic front to really spur them on to do better and improve. Sure, Rodgers plays an expansive style that is wonderful to watch but it is heavily predicated on the individual genius of the likes of Moussa Dembélé and Kieran Tierney.
What happens when they leave? As will inevitably happen in the summer? Replacing a talent like Dembélé requires supreme scouting, and it would be an essential signing. Rodgers' history at Liverpool showed how quickly things can implode without an all-singing all-dancing superstar forward.
Celtic have been a wonderful rehabilitation for Brendan Rodgers' career after those Anfield horrors, but he's taken the Glaswegians as far as he can do with things as they currently are. Barring a gargantuan investment of cash to allow massive player recruitment (as well as replacing Dembélé, etc.), they won't significantly improve.
If Rodgers truly wants to progress as a coach then he needs to move on at the end of the season.
Where? Perhaps by then West Ham will be sick of David Moyes. Or Sam Allardyce will have left the newly monied Everton? His time at Celtic has reminded everyone just what he is capable of. Either way, if Rodgers has designs on greater success, his future likes away from Celtic Park.