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I don’t think Arsenal will win another Premier League title under Arsène Wenger. Not the Wenger who is so obsessed with youth and potential that he refuses to accept the value of experience and short-term solutions. Not the Wenger who stubbornly sticks to his principles, even though Arsenal are going backwards as their rivals evolve and improve.

It’s amazing how quickly things can unravel. Wenger is already at the dangerous stage where a single game takes on huge significance: tomorrow’s match against Manchester United. If United win well at the Emirates, Wenger will face a backlash from all corners.

It’s naive to think he has a job for life because of his achievements. That rightly buys him time, but questions will be asked within the club if the team don’t look like challenging for the league. And they don’t: they seem weaker and easier to beat than last year. Of the present side, probably only Cesc Fàbregas would be good enough for that “Invincibles” line-up from 2003-04.

Wenger must know the value of a tough defence because he inherited one when he arrived at the club, so why has he allowed his back line to become so frail?

The manager’s saving grace is the Champions League. As long as Arsenal are in that, he’ll be OK. But while the knockout format allows flawed teams to hide their shortcomings over a two-legged tie, to progress you also need a bit of luck. If Arsenal go out in the next round and still look indifferent in the Premier League, I think Wenger will go at the end of the season.

Sir Alex Ferguson faced similar pressure at United in 2005-06, when after an early exit in Europe and finishing a distant second in the league, there was a growing belief that his time was up. What happened? Ferguson solved the problems and won the league the next season.

Wenger needs to prove that he can adapt in adversity like his great rival. He transformed English football; now he’s the one who has to change. Accepting that would be a sign of the intelligence he possesses. He has to go to his board and say what they may already be thinking: “I’ve made mistakes, the make-up of the team isn’t right and I need money to sign experience in January”. Then he has to make bold statements by bringing in players who can make a massive impact, shaking up the side by adding some character.

Think of what a good loan signing Henrik Larsson was for Ferguson, of how Paolo Di Canio briefly galvanised Charlton Athletic, how Jürgen Klinsmann lifted Tottenham Hotspur. These type of men are out there and Wenger has to find them to make up for earlier failings such as believing that the likes of the lightweight Denilson would be good enough to replace Mathieu Flamini when Arsenal should have outbid Liverpool for Javier Mascherano. Too expensive? How costly would failing to qualify for the Champions League be? And why was Wenger prepared to buy big in the past — remember Sylvain Wiltord — but won’t now?

He has been a genius but unless Wenger can rediscover a sharp edge to go with his side’s pretty football, Arsenal will fall away and they will be looking for a new manager.