There was an opportunity, after 28 minutes when Andriy Arshavin went off injured, to introduce Walcott ahead of substitute Emmanuel Eboue.

What Arsene Wenger had already seen, however, probably coloured his judgement. He had watched Barcelona take his players to the cleaners, certainly in the opening 15 minutes, and was, perhaps for the first time this season, purely fearful of the flair of the opposition.

So he played Eboue, a midfielder with a defensive instinct, rather than Walcott, a winger with a yen to be a forward.

He deployed a player who could shore the game up, limit the damage and hit on the counter-attack, rather than the flying machine. And not until Arsenal were two thoroughly deserved goals down did Wenger acknowledge that, in Walcott, Arsenal possess a unique weapon.

Walcott does not have the mind of Lionel Messi, his brilliance, the wonderful rhythm of his play, but he does have a talent that is the enemy of defenders everywhere: pace.

Raw, uninhibited speed that electrified Arsenal’s attack when he arrived and sparked this incredible revival.

Walcott changed the game. Not just because he scored, but because he altered the dynamic and gave Barcelona a problem equal to the challenge that faced Arsenal. Suddenly, they had this little rocket to control. It put them on edge and they threw the game away.

Although Arsenal were afforded the time to recover from a shaky start against Barcelona, if David Haye suffers a similarly inadequate beginning when he fights John Ruiz on Saturday then he will leave himself susceptible to losing his title belt. Former British and European light welterweight champion Clinton McKenzie, writing in the Daily Mail, has warned Haye about the dangers of underestimating Ruiz:

Haye now knows he can box, that's for certain, and he know how to keep out of trouble and when to use his brain. The upshot of that is, hopefully, he won't always go flying in now, looking for a knockout inside the first few rounds.

But also, I hope he doesn't underestimate Ruiz because he's been around for a long time - particularly at heavyweight. He's a tough old boot who has fought some of the best in the category and he's very capable of giving Haye more than a little test.

Ruiz knows the weight, he knows the ropes and he has got a few tricks up his sleeve which can cause Haye a few problems. I want to see how Haye deals with that.

Ruiz isn't going to be the one to try to force an error. He's going to let Haye do his thing and then try to capitalise on what mistakes the champion makes.

And like all of the best heavyweights, he comes to fight, he doesn't hide and Haye will have to find his very best shot to put him down and keep him down.

All credit to Haye for winning a world title and we saw him out partying loads afterwards, but that's his call. But it has sunk in a bit now and he realises that he got to get down to work.

It's too early to say whether Haye has got it in him to hang around as world champion for a number of years. And until he beats Vitali Klitschko he has plenty to prove. Beat Klitschko and then he will have proven his ability.

Haye, for me, remains at a crossroads. Until he gets a few more wins under his belt, he's still proving himself and he needs more fights to find out what heavyweight boxing is all about.