Apparently United gave away 17,500 free tickets for the game against Astana the other week. How true that is, I don't know but they obviously gave a fair chunk of freebies out. They do it a lot for early round League Cup games too - you can easily tell because if they happen to be on the box, you can hear thousands of screaming schoolkids counting down the clock to half-time!
I don't know how many tickets United gave away for Astana but the crowd was still only 45/50,000 for that game. Where have the billions of fans gone...haha!!.