2685
http://www.manutd.com/en/Tickets-And-Hospitality/Tickets-And-Hospitality-News/2015/Jul/Champions-League-Away-Game-Information.aspx
On a side note, they get a full breakdown of how many are on each credit. Imagine that.
Feel dirty likewise by clicling on that, but noticed a good and honest way they showed how many people have a number of credits:
128 supporters have 10 credits
28 supporters have 9 credits
341 supporters have 8 credits
60 supporters have 7 credits
314 supporters have 6 credits
201 supporters have 5 credits
554 supporters have 4 credits
839 supporters have 3 credits
1,952 supporters have 2 credits
3,600 supporters have 1 credit
173,829 supporters have 0 credits
Seems a pretty well run ticket office compared to ours..
I'll go take a shower now for praising the mancs..