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,

The last four teams standing return to play in the UEFA Champions League this week for the first leg of the semifinals, when some of Europe's top sides will begin to map out their route to the final on May 31 at Munich's Allianz Arena.

Inter arrives in Barcelona under difficult circumstances. The team has lost three straight matches without scoring a goal — something it hasn’t done in over 13 years.