Here are 5 things to watch for in the Champions League this week.

The Champions League semi-finalists will be determined this week through the four second leg ties from the last eight.

This is what to look out for during the action.

Match of the Week

The most delicately poised quarter-final showdown will place at San Siro, where Inter host Bayern Munich, who lead 2-1 courtesy to Davide Frattesi's late victory in Germany.

That ended Bayern's five-year, 22-game unbeaten streak at home in Europe, leaving them with a difficult challenge in Milan, despite winning all four of their previous road games against Inter.

However, of the 23 prior occasions in this competition that the Nerazzurri have held a first leg lead, they have advanced in 21 of them, albeit one of those eliminations did come last season against Atlético de Madrid.

The last six meetings between the teams have also resulted in three wins each, keeping this one very much open and all to play for.

🔎 Team to watch.

How Aston Villa fans dared to dream in Paris last week when Morgan Rogers gave them an all-too-brief lead against PSG, and the home side's late third goal in a 3-1 victory was a deadly blow that may have put the tie beyond reach.

"We have enough quality to cause any team in the world problems," Villa's goal scorer insisted. "We've got nothing to lose so why not go for it?"

With the support of a loud Villa Park, things may get interesting if the hosts can score the first goal, and there are reasons to be optimistic.

PSG has won only four of their 17 trips to England, and they have been eliminated three of the seven times they have taken a two-goal lead into the second leg, while Unai Emery has lost only one of his previous 13 home games in European play.

Don't write off the Villans just yet...

🔥 Player to watch.

Raphinha, the Barcelona standout, is having a fantastic season in this league.

In 11 Champions League games, he has been personally involved in 19 goals, scoring 12 and contributing seven assists.

If he scores or assists a teammate in Dortmund, he will become only the third player behind Cristiano Ronaldo and Robert Lewandowski to have a season with 20 or more goals in Europe's top league.

In 2013/14, the Portuguese superstar scored 21 goals, setting a season record. With the longer format, may Raphinha shatter that record this year?

Potential upset.

It isn't often that Real Madrid emerges triumphant from a Champions League knockout match, but their terrible performance and 3-0 loss in London has left them with a difficult task against Arsenal.

However, this is Real Madrid at home on Champions League night. Things happen in these circumstances that cannot be explained, and Manchester City, Bayern Munich, and others can attest to being left punch drunk by a thrilling Real Madrid comeback when all hope appeared to be lost.

Since the start of 2015/16, Los Blancos have played 16 second leg knockout ties at home and have only failed to advance once, despite the fact that the circumstances are even more challenging this time around.

If they do it, it could be their most impressive escape ever.

📊 A fascinating statistic

Last week, Arsenal extended their unbeaten streak against Real Madrid to three games, and they might become the first team in Europe to keep four consecutive clean sheets against the record holders.