Wojciech Szczesny has revealed that Arsenal's defensive problems this season mean that they go into the north London derby at Tottenham Hotspur on Sunday having switched from a zonal to a man-marking system. Arsène Wenger decided on the change following the 4-3 defeat at Blackburn Rovers a fortnight ago. Those goals made it 14 conceded by Szczesny in the league after four games.

The Polish goalkeeper admits a preference for zonal marking, but he is happy with Wenger's decision. "I really don't mind as long as it works. I personally prefer zonal marking but it is the manager's decision what we are going to do," he said.

"We have decided to change it since Blackburn. It really doesn't matter what you do as long as you do it correctly and it works. I think zonal works better for us. We have worked on it during pre-season where we never conceded from a set piece and it looked like it was working.

"We did concede a stupid goal at Blackburn [Alex Song's 50th-minute own goal when no defender dealt with a free-kick] and I hope the man-marking will work for us now."

The third goal allowed by Arsenal that day was also due to lax defending as Laurent Koscielny allowed a high ball to pass him at a corner. Szczesny admits that their problems from dead balls and aerial deliveries are now acknowledged by the squad and manager.

"We do realise what our weaknesses are and defending set pieces was our weakness last season. We spent a lot of time working on it during pre-season and we can only get better on it as time goes on," he said.

Szczesny cited Gaël Clichy's departure for Manchester City, Per Mertesacker's arrival in August and Thomas Vermaelen's long-term injury absence as factors in Arsenal's poor defensive record. He said: "It's a new defence and some of the players have to get used to playing with each other. You can see from game to game we are getting better, but it takes time. I hope we can avoid all the mistakes that we have made at the beginning of the season and if we stick together and keep working hard I am sure we are going to have a lot of clean sheets by the end."

The injury list at Arsenal is a long one. While tests to Theo Walcott, who has a knee problem, Gervinho (muscular), and Koscielny (ankle), will establish if they can play at Spurs, Johan Djourou, Yossi Benayoun, Jack Wilshere, Sèbastien Squillaci and Abou Diaby are all unavailable for selection.

Last season the two league fixtures between the old rivals ended with a 3-2 win for Spurs at the Emirates and a 3-3 draw at White Hart Lane. Regarding those four dropped points Szczesny said: "It doesn't really make a difference because when you go to White Hart Lane you forget about everything that happened in the past. It is all about being switched on and being focused for the game. If we are at our very best I am confident we can get the three points."

"It is a game you always look forward to playing in. You train every game to play in those kinds of games. There are a few players who have never played at White Hart Lane and it will be a new experience for them. I am sure everyone will be at their very best."

Emmanuel Adebayor faces his former club for the first time in a Spurs shirt and Szczesny, who arrived at Arsenal a year before the striker departed, is keen deny him a goal. The 21-year-old said: "I would love to keep a clean sheet against him, I'm not going to lie. But I am very confident we can do that and get the three points. He is a quality player – probably one of the best strikers I've ever trained with. We won't approach the game in a different way than we usually do. Ade is a great striker and we know how dangerous he is but it is to our advantage that we know how to deal with him. I'm not going to tell you because it's our little secret."

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