If not, the only way you can get tickets is from touts, which I would not recommend but there are usually some wandering around outside Old Trafford before the game.
I would recommend becoming a One United member if you want tickets. Not only will this mean you can apply for every game but you can also buy tickets from season ticket holders that can not make the game, through the ticket exchange service run by Viagogo, if your application is rejected. I think it costs about Â£28 per person but you get a welcome pack with free gifts, discounts, free entry to reserve games etc.
One of my friends became a One United member towards the end of last season purely because he wanted a ticket for the Champions League semi-final against AC Milan and he got one.
A forum community dedicated to Manchester United owners and enthusiasts. Come join the discussion about Manchester United football, players, reviews, matches, live games, scores, jerseys and much more!