Graeme Souness: We'll learn more about in-form Arsenal against Napoli

Arsenal v Napoli

Celtic v Barcelona

Barcelona may have set a club record for their best ever start to a La Liga season, but I'm still not convinced by them. There's still a concern for me at the back - Marc Batra and Gerard Pique are still vulnerable in my opinion. I think they're both very good with the ball, but I don't think they're great defenders. And the injury to Lionel Messi is enormous; we saw that last year when they played Bayern Munich without him. He is their number one threat. If he keeps getting muscle injuries then we'll find out in this coming season how vital he is to Barcelona because he's such a special player for them. In the tight games he's the one who makes the difference. People say he's the best player ever - but that's a debate for another day. Nevertheless, Celtic are going to spend the vast majority of this game without the ball and will be relying on getting something from a set piece or a counter-attack. Personally, I think Barcelona will have learned from this fixture last season when they were caught out by a corner and Tony Watt's goal on the break.