Bayern Munich v Arsenal: Wojciech Szczesny talent not in question, but mistakes cannot be ignored

Wojciech Szczesny was meant to be in goal tonight. The Polish goalkeeper, who revels in having the football world at his feet, would have loved to be in the Allianz Arena to face Bayern Munich. Had he been performing at his best, he surely would have been.

However, Arsène Wenger left him at home while, contrary to speculation which had suggested that a number of senior players would be left out in what was an essentially futile cause, the manager otherwise chose a full-strength team.

Wenger insisted on Tuesday this was to do with fatigue. "He has played many games since the start of the season," he said. "Recently I felt that mentally it affected him, that is why I have decided to rest him."

Szczesny is struggling, but there is a sense that it owes at least as much to lack of form and confidence as to tiredness. He is not the only offender but the keeper's errors have been a major part of Arsenal's dismal defence this year. Talent has never been an issue – he is quick, strong, agile and brave. But his concentration is not perfect and the mistakes have been coming for nearly a year.

These things are hard to pinpoint but it might well have started in a 3-3 draw with Norwich last May. With Arsenal 1-0 up in the first half Szczesny let a gentle Wes Hoolahan shot through his arms, and despite the best efforts of Robin van Persie they dropped valuable points.

Worse was to come in the European Championship last summer. In the opening game at the National Stadium in Warsaw against Greece, one of the biggest matches in Polish history, Szczesny let in a soft equaliser before making a clumsy tackle on Dimitris Salpingidis and was sent off. He did not play another minute in the tournament.

That would hit the confidence of any 22-year-old. This season he has never seemed as assured as he did last year, and his mask of bravado looks increasingly out of place when the substance is not there behind it. Young goalkeepers do make mistakes, but Szczesny has made more than enough this year to raise doubts whether he is the long-term answer for Arsenal.

In September, he let Danny Fox score a comically easy goal in Arsenal's comfortable 6-1 win over Southampton, but it has been since the turn of the year that his performances have seriously dipped. Szczesny conceded an avoidable penalty in the 2-1 defeat at Chelsea on 20 January, bringing down Ramires and just avoiding a red card.

Last month Blackburn Rovers came to the Emirates for an FA Cup game that should have been an easy home win. But Blackburn knew Szczesny was vulnerable to palming shots back out in front of him, and the planning paid off: Martin Olsson's shot was spilled, Colin Kazim-Richards followed it in and Arsenal were knocked out of the Cup.

One week later, Andreas Weimann surprised Szczesny from distance, striking the ball through his hands for Aston Villa in a game that Arsenal dug out to win 2-1.

So Wenger picked Lukasz Fabianski instead. Blackburn and Villa are one thing but Bayern clearly quite another. Maybe Wenger thought that it was in the young goalkeeper's best interests.