As two of the most colossal fanbases on the planet, we're not sure we want to get in the way of this one.
But there's an almighty "who said it?" debate erupting on Twitter following a gesture from Manchester United.
Ahead of the their closed-door Premier League return to Old Trafford on Wednesday night, the club have adorned seats with a banner featuring a quote from legendary boss Sir Matt Busby.
Or does it?
Placed behind the goal at the Stretford End, the banner reads: "Football is nothing without fans - Sir Matt Busby".
That's, of course, a slightly rearranged quote Celtic fans will recognise instantly.
The words are immortalised outside Celtic Park in tribute to Jock Stein, and they read: "Football without fans is nothing."
It's an iconic phrase for the Parkhead faithful and, upon clocking United's display on Twitter, it's fair to say they weren't having it being attributed to Busby.
A sceptical punter wrote wrote: "I'm sure Matt Busby definitely said all those words but just not together or in that order."
Another said: "The legend that is Mr Jock Stein uttered those words long before Busby. Just saying."
One said: "Jock Stein, Matt Busby, both Scottish, nobody will notice."
Another added: "Matt Busby didn't say it though, Jock Stein did and it's 'Football without fans is nothing'. Other than that it's a good point."
One wrote: "As said by one of Sir Matt Busby's closest friends and a personal hero to your greatest manager, his name, Jock Stein."
There were plenty more where this one came from as another added: "You're going to need a bigger boat - Sir Matt Busby"
Another said: "One small step for man, one giant leap for Mankind - Matt Busby"
Another one? One fan said: "Ich bin ein Berliner – Sir Matt Busby"
And finally, this cracker: "As far back as I can remember, I always wanted to be a gangster – Sir Matt Busby"
