Any series ends sooner or later and it would be interesting to "catch" this moment. Let's assume that with a minimum odds of an underdog winning against Barcelona of 4, we have three attempts to guess this moment and be in profit by at least one bet (if the third bet wins). But now there are two obvious matches ahead where Barcelona can lose - against United and against Real, I doubt that the odds of United and Real to win in them will be much more than 2.
Losing points is still very likely to be felt by Barcelona even though they are currently in a very good trend. Talking about this is football, sometimes luck and bad luck will be experienced by a team with their good performance or with their bad performance. What Xavi Hernandez can do is motivate his players to stay focused on the game, be it when facing a strong team or a weak team.
If I remember correctly, Barcelona this season from the big games got the following results: 4 defeats in the Champions League (formally one draw, but equal to a defeat), a defeat against Real Madrid, a victory over Atlético and a victory over Real Madrid. With United they drew, but since this is a home game, it is a failure. It is reasonable to assume that since Barcelona has so many failures in big games, but is now so praised for its success in La Liga, that the odds on its opponents in games with United and Real Madrid will be very attractive. These are the betting considerations that interest me most of all.