Rival fans did not let go of the opportunity to mock Celtic and social media was buzzing with their witty responses.
A Rangers fan, @HappiestPants, wrote: "FOUR? Nah this can’t be, Rangers went to Germany and HAMMERED a far superior Dortmund team, what’s going on?! Celtic are an embarrassment to Scotland!!"
Meanwhile, @RG72_, wrote: "Generational hate watch cheers lads."
Meanwhile, @unsynq, wrote: "5-1 down at half time..And people thought you's would do well in the Prem. The Championship would be the right level for Celtic."
@ryanward5_ opined: "Celtic are a waste of time in the Champions League like. Might as well give it to another Prem team."
Whereas, @ExpressionsOOZ, wrote: "Celtic go from Man City in their league to Southampton in the Champions league it’s crazy."