Image source, Getty Images

How do you replace a guy like Lionel Messi? The Argentina international has been ruled out for seven to eight weeks, and tonight 20-year-old forward Sandro joins Luis Suarez and Neymar in Barcelona's attack instead. 

Former Manchester United striker Javier Hernandez starts up front for Bayer Leverkusen.

Barcelona XI: Ter Stegen, Alves, Pique, Mascherano, Mathieu, Rakitic Busquets, Iniesta, Suarez, Neymar, Sandro.

Leverkusen XI: Leno, Donati, Tah, Papadopoulos, Nascimento Borges, Bender, Kramer, Kampl, Calhanoglu, Bellarabi, Hernandez.

Arsenal

Petr Cech is left out of the Arsenal side tonight as David Ospina looks to have been given the 'cup keeper' role.

Full team news to come. 

Chelsea

We expected changes from Jose Mourinho and the big news is that he has left out Eden Hazard tonight.

The Belgian has not been near his brilliant best this season and is benched.

Full team news to come.

Luis Enrique.

Pep Guardiola

Jose Mourinho.

Arsene Wenger.

Image source, Reuters

All wonderfully successful, all serial winners. Some more financially prudent than others. Some better at developing youngsters. Some better with the media.

But who would you prefer at the helm of your club?

Vote now on this page.

Terms and conditions.

BBC Radio 5 Live

Join BBC Radio 5 live for build-up to tonight's Champions League fixtures from 18:30 BST.

The main commentary game will be Porto v Chelsea, but there will also be updates from Arsenal's home match with Olympiakos.

And later you can call in and have your say with the 5 live Football Social from 22:00.

Chelsea's poor start to the domestic season may have drawn all off the headlines but on the European front it was Arsenal who got off to a shocker.

Their 2-1 defeat in Zagreb last time out means that there is zero room for error against Greek side Olympiakos this evening. 

Can they pick up a much-needed three points?

Image source, Reuters

It seems hard to comprehend now, but Jose Mourinho was a relatively unknown, young coach when he has handed the Porto job in January 2002.

Porto were fifth in the league, below Mourinho's then-side União de Leiria, out of the Champions League and out of the cup.

Within two-and-a-half years Mourinho guided Porto to two league titles, the Uefa Cup, and the Champions League.

An awesome achievement.

Image source, AP

The rest,as they say, is history.

More league titles (six of 'em), another Champions League, plenty of spats...

Tonight the 'Special One' comes home with his current side in a sorry state.

Is tonight the night Mourinho begins to become special again?

Image source, PA