Sir Alex Ferguson has launched a fierce attack on the design of Emirates Stadium as Arsenal promised to lay on extra security for Manchester United's visit tomorrow lunchtime.

The United manager is still unhappy at the alleged abuse his team's substitutes and staff received at the ground last season.

Arsenal responded by increasing the number of stewards protecting the Scot and Arsene Wenger today urged supporters to leave Ferguson alone.

But the United boss was dismissive of the new security plans, and claimed the design of the £400million ground was fundamentally flawed.

His comments will only inflame a match already described as a "must-win" for Arsenal by Wenger after their stumbles against Spurs and Stoke.

Ferguson said: "It was nasty last year. It was pretty unsavoury.

"You build a modern stadium like Arsenal have done and it's a weakness when you you don't provide safety for the visiting team's substitutes and staff. But it's too open for my liking. You need tin helmets."

In the wake of last year's incident, Arsenal told United at the time that they felt there was "ample" protection for Ferguson but have now reviewed the situation.

An internal Arsenal inquiry concluded that the fans were chanting only "Taggart'' at Ferguson during the 2-2 draw last season, and cameras even picked up a United security man turning provocatively to home supporters after Cristiano Ronaldo scored.

But an Arsenal spokeswoman said: "There will be an extra three stewards in the 'paddock', the row behind the dugout, making five stewards in total. At the back of block 32 [where the away dugout lies], there will be an 'ejection squad' viewing the fans in case there is any issue.

"In addition to those provisions, there will be somebody in the control room watching an extra camera that will be monitoring the situation around the dugout.

"It must be stressed that we have never had any problems other than this one [last year] and we are all hopeful that the game will go off peacefully.''

This is the first time Arsenal have rearranged their security arrangements for one specific manager and Wenger said he hoped the fans would show Ferguson some respect.

He said: "We always want to respect our opponents and respect the dugout because the way we want to behave at Arsenal is to respect everybody."

Last weekend's defeat by Stoke means the Gunners need a win to get themselves back into the title race and Wenger accepted that a draw will not be enough tomorrow.

He said: "We have to win the game. We will not be happy with a draw because you cannot play at home and not go for the win. It is a big game and you cannot be happy with a draw.

"I cannot put any percentage on that but it is a big game and it is important. This game is welcome because many people doubt our capabilities in the big games and I don't because I believe we will do well. What you want is the chance to show how good you are, enjoy it, put on a good performance and I know we have a good chance to beat Man United."

Ferguson also rejected the idea that his side were favourites. He said: "If you look at Arsenal and Manchester United games over the years you know they are always highly competitive. If anybody thinks we are going to the Emirates Stadium thinking we are going to have an easy game because they are missing a couple of key players then they are mistaken."

Wenger will make late fitness decisions over Mikael Silvestre (broken nose) and Theo Walcott (shoulder) but it does appear that Carlos Vela and Nicklas Bendtner will start the match in attack with Emmanuel Adebayor (injured) and Robin van Persie (suspended) missing.