They love their late night football in Spain - and we could be looking at a finish time of around midnight local time if this goes all the way. It starts at 21:15 local time. 

If Real Sociedad lead 1-0 after 90 minutes, there will be extra time. Away goals count as double. If needed, penalties will be used to determine the winners.

It could be a long night so pull up a chair and mug of hot chocolate. We're about to get going

Watch out for Willian Jose. Real Sociedad's Brazilian forward has scored nine goals in 17 La Liga games this season, including one against Barcelona in November. 

Image source, Getty Images

Image source, Getty Images

Right, the Nou Camp is filling up and we're only a few minutes from the start.

Do Real Sociedad stand any chance of overturning a 1-0 deficit away to Barcelona?

They've beaten Barca in four of the last eight top-flight meetings. However, they were all in the Basque Country and Sociedad have conceded 22 times in their last six La Liga visits to Barcelona's ground.

Sociedad are much improved from when David Moyes was sacked by them 14 months ago, with the club only outside the relegation zone on goal difference.

Under former Barcelona midfielder and assistant Eusebio Sacristan, they are chasing a Champions League spot and sit fourth in La Liga, eight points behind leaders Real Madrid.

One win in five games, out of the Copa del Rey, treble hopes down the drain.

So we want to know the answer to this question: Are the wheels coming off Real Madrid's season?

Let's hear from you. Tweet #bbceurofooty , external

What has happened to Real Madrid?

They started 2017 with a three-point lead at the top of the table - with a game in hand on their rivals - and with dreams of landing a La Liga, Champions League and Copa del Rey treble.

Less than four weeks into the new calendar year, Real find themselves out of the King's Cup and their La Liga lead now down to a single point after the end of Zinedine Zidane's side's 40-match unbeaten run in all competitions.

A Real wobble?

Image source, AFP

Image source, Rex Features

What's this? Barcelona have their own branded crisps on sale outside the Nou Camp. 

Wonder if Manchester United's commercial team have cottoned on? It could be another tasty earner to go with their official mattress and pillow partner. 

Luis Enrique makes four changes to the side that started the 1-0 first leg win in San Sebastian last week. Midfielder Denis Suarez starts as do Javier Mascherano, Jordi Alba and Andre Gomes. Out go Lucas Digne, Sergio Busquets, Andres Iniesta and Ivan Rakitic.

Barcelona XI: Cillessen, Roberto, Pique, Umtiti, Alba, Denis Suarez, Mascherano, Gomes, Luis Suarez, Messi, Neymar.

Real Sociedad keep the same side that started the first leg.

Real Sociedad XI:  Rulli, Elustondo, Navas, Martínez, Yuri, Illarramendi, Zurutuza, Vela, Prieto, Oyrarzabal, Jose.  

Image source, Rex Features

That feeling when you've had a rubbish week but then realise Messi, Suarez and Neymar are all playing on Thursday...for a place in a semi-final.

Image source, Rex Features

We know the identity of three of this season's Copa del Rey semi-finalists.

Celta Vigo stunned 19-time winners Real Madrid 4-3 on aggregate, while Atletico Madrid are also through along with Basque Country club Alaves.

But will it be Barcelona or Real Sociedad joining them in Friday's draw?

Inquests are under way in Spain's capital city after it all went wrong for Real Madrid.

Image source, Getty Images

Sevilla and Villarreal have also botched up winning Spain's oldest football competition.

Image source, Getty Images

The door has been left wide open for holders Barcelona to claim a record 29th Copa del Rey title. Will the King's Cup be staying in the hands of Luis Enrique's cup kings?

Image source, Getty Images