How does it work?Thirty-six sides entered into the new "league phase" and now just four remain with a month-and-a-half to go in the UCL campaign.Barcelona, Paris Saint-Germain, Arsenal, and Inter Milan are through to the semifinals,

As Inter prepare to host Barcelona for the second leg of the Champions League semi-final in San Siro on Tuesday night, here is a look at the key battles to keep an eye on after the thrilling 3-3 draw