I'm not sure we could yet, it'd have to be a very off day for Barca. Our best hope would be to catch them on the break then defend vigorously. A draw is more realistic (and would be a great result), we showed against Arsenal and others last season that we have one of the strongest defensive setups in Europe as the best defensive unit in the Premier League. But we have played against no one close to the level of Messi in the Premier League. We have as good a chance of any at beating, especially if we become faster on the counterattack, but it is still quite a small chance just like it is for any team in the world.