Ian Dennis
BBC Radio 5 live senior football reporter at Stamford Bridge

Image source, Getty Images

"When you question what the official on the goal line does, he has just done his job. It did cross the line by about a foot in the end."

"Theo". "Theo". "Theo".

"Get the number 14 and tell him to track back, lads..."

Image source, Opta

It is all Olympiakos at the moment. 

A nervy moment for Arsenal as Kostas Fortounis falls over inside the area. He wasn't even that close to Theo Walcott. The referee blows his whistle, walks straight over...and books Fortounis for diving.

Chelsea's defence is worryingly pedestrian. 

There's no urgency or desire to press as Porto patiently pass the ball around the edge of the area, and it almost proves costly as Yacine Brahimi is given the chance to have a crack at goal at Thibaut Courtois' near post, but the Chelsea keeper is alert enough to thump the ball away.

Since Theo Walcott was clattered, Arsenal have not bothered attacking down the right...

Image source, Opta

Image source, Get

Arsenal have nothing to worry about, Brown Ideye is up front for Olympiakos.

He managed seven goals in a season at West Brom before being shipped off to Greece during the summer.

Great headphones though.

Image source, Getty Images

Very hostile atmosphere in Athens as every touch of the ball by an Arsenal player is greeted by a chorus of boos. Theo Walcott is clattered as Olympiakos players make their presence known. No clear-cut chances as yet, though.

Early chance for Chelsea as Willian swings a free-kick into the area from midway inside the Porto half. It deflects behind for a corner, but it comes to nothing.

Mark Lawrenson
Former Liverpool defender in Greece

"I think this stadium is worth a goal start as well as the advantage they already have."

Image source, Reuters

Here we go. Games across Europe are getting under way.

Tell us or, if you are feeling creative, draw what it would be and send to #bbcfootball., external

You can also text in on 81111 (UK only) and post on the Match of the Day Facebook page.

This is a fancy drawing indeed. We can see Louis van Gaal and assume this is Memphis Depay?

Is he handing him over? Giving him back?

Image source, Getty Images

Will Chelsea and Arsenal avoid following Manchester United out of the Champions League and into Thursday night football? 

We'll find out soon enough, with kick off almost upon us.

John Murray
BBC Radio 5 live commentator in Greece

Image source, Reuters

"It's quite a sight in this stadium. The teams walk slowly out. I'm watching Petr Cech and Per Mertesacker flexing their muscle. This stadium is wonderfully atmospheric, it's relatively new, there are streamers coming from the back of the stand to the front. Arsene Wenger said it would be hostile and so it is."

Don't worry Matt - you're out on your own.

Intimidating stuff at Olympiakos.

Both sets of teams wait in the tunnel, a banner with the words "we rule this land" hangs above the exit onto the pitch. 

As the players walk out, the home fans hold up white and red flags, with huge cheers as the home team emerges. 

John Bennett
BBC World Service in Valencia

"The photographers are ready for Gary Neville. A big moment for Neville was a first ever team selection, it contains two changes. It's a must win, Valencia have to beat Lyon. What will he be like in the dugout? The Mestalla - and some of Spain's most volatile support - is ready."

Spanish football journalist Mike Holden at the Mestalla: "Two changes from Saturday's 1-1 draw with Barcelona. Ruben Vezo is suspended, so in comes Joao Cancelo at right back. Shkodran Mustafi returns from hamstring trouble and will partner Aymen Abdennour at centre back, meaning Anderlan Santos drops to the bench. Looks like 4-3-3 again."