The champions of England and Scotland take on each other on Tuesday, in a Champions League battle of Britain.
Manchester United are the hosts for the match, with Celtic hoping to end a dreadful away record in European games.
They have yet to win a match away from Celtic Park in the Champions League, while United haven't lost in their past 16 home matches in the competition.
The teams did meet at the same stage two seasons ago, when both sides won their home games.
That wasn't the last time a team from Glasgow came to Manchester though, with city rivals Rangers making the trip earlier this year.
That was for the final of the Uefa Cup in May, against Zenit St Petersburg, and as many as 100,000 Rangers fans travelled to Manchester.
Some of those supporters caused loads of trouble in the city, after giant screens set up to show the match to fans without tickets broke.
Police in Manchester say they don't expect there to be those sort of problems this time, as it is just a normal Champions League match, not a final.
And Celtic fans without tickets have been told to stay away from the match, as there aren't big screens for fans to watch the match on.
Arsenal are also in action in the Champions League on Tuesday, when they take on Turkish side Fenerbahce.