Arsenal's defence are making too many individual errors to leave them exposed regardless of Arsene Wenger's tactics

Losing Alexis Sanchez is a disaster for Arsenal but how much does any change in their front line matter when their defence is this bad? The story of Arsenal’s typical mid-season stumble this year has been the collapse of their defence and their failure to keep out even the most modest opposition.

What so infuriated Arsene Wenger on Sunday afternoon was how they gifted two goals to a Bournemouth side who had never looked like scoring. There was no real pressure, no great siege, but defensive errors still coughed up two massive chances within four second-half minutes. And a 1-0 lead became a 2-1 defeat. All this against a team with one league win in the last two months.

Wenger came in to his post-match press conference bemoaning how his team had gifted Bournemouth the goals. “We made mistakes in areas where you wonder where they came from,” Wenger said. “Two very surprising mistakes, not even forced errors. Just a lack of the right decision-making.”

But what was surprising about this? Arsenal have taken two clean sheets from their last nine Premier League games, and they were against free-scoring Newcastle United and West Ham United. They are coughing up big chances over and over again, almost no matter what system they play.

Wenger wants to play a 4-2-3-1 system at the moment to make sure that his team keeps producing chances. But there have been times when it has just left his team too open at the back. Like the 3-3 with Liverpool on 22 December, when he played a back four and Liverpool should have won the game by a distance.

Days like that have forced Wenger back into a back five, giving him an extra centre-back to try to stem the flow of the chances. But what use is an extra defender when they make such bad mistakes? Too many Arsenal games in the last few months have seen individual errors, not down to any tactical plan, costing them the game. Like the 3-1 defeat by Manchester United on 2 December, when Arsenal had the extra defender, but Sead Kolasinac and Shkodran Mustafi gifted United a two-goal lead in the first 10 minutes. Or the 1-1 draw at Southampton eight days later when Per Mertesacker was drafted in but left Arsenal desperately vulnerable at the start.

Even at Selhurst Park on 28 December, the day of Sanchez’s last two goals for the club, Arsenal were poor at the back despite the extra defender. It was too easy for Andros Townsend to finish from Wilfried Zaha’s low cross and you wondered what the point was of Arsenal having three centre-backs when they were this easy to play through.

Back with a patched up back four at the City Ground last Sunday, Arsenal put in one of their worst defensive performances of the season losing 4-2, in a game where they could have conceded twice as many. It was not their first choice, but Rob Holding and Ainsley Maitland-Niles both played, and they are now part of the Premier League team.

The three-man combination of Rob Holding, Shkodran Mustafi and Calum Chambers did well at Stamford Bridge on Wednesday night but at Bournemouth on Sunday they couldn’t produce the same performance, making the simple mistakes in the box to cost Arsenal the game. Holding and Chambers have struggled at times this season and it is not easy being a young defender in this team. Mustafi worked hard to organise and drag his team-mates with him, taking far more leadership responsibility than Laurent Koscielny ever does.

But this is not a team focused on defence and it has not been for years. As Wenger joked recently, he would like to play just one defender if he could get away with it. But in the real world, this team has lost its spark up front, so it needs to keep goals out. And at that they are desperately struggling.