The duo renew the Barclays Premier League's most enduring and ferocious managerial rivalry when they lock horns in tomorrow's seismic FA Cup fifth-round clash at Old Trafford.

Wenger, 58, has three years remaining on his contract at Arsenal and refuses to consider retirement while he continues to relish competition against adversaries such as Ferguson.

And the Frenchman believes it is that same motivation that drives the durable Manchester United boss.

"I was asked yesterday when I want to retire and I said 'I don't know'. It could be tomorrow, it could be 10 years," he said.

"You must be destroyed when you lose and happy when you win in this job. It feels like that but that's why you are in the job.

"It's a balance between internal desire, that instinctive animal desire to fight and win, and being wise enough to make the right decisions.

"You continue because of a mixture of things, but you must have that physical drive to want to win and be able to last the distance under pressure.

"Of course that is why Alex Ferguson is still doing the job.

"As long as winning means something to you, you go for it because you sacrifice nearly everything for the next game and you live life like a professional football player.

"That means if it's not so important any more you are not ready to sacrifice, to not go out and prepare like a player.

"You only do that because it has massive meaning for you to win."

Arsenal's desire to gain a precious victory over United will be tested to the limit after being struck by a succession of injuries.

They travel to Old Trafford with just 14 fit outfield players with eight members of the squad definitely missing and another four rated doubtful.

There are question marks over Gael Clichy, Philippe Senderos, Emmanuel Adebayor and Mathieu Flamini, who will all undergo fitness tests tomorrow.

Definitely out through injury or unavailability are Bacary Sagna, Theo Walcott, Johan Djourou, Alex Song, Robin van Persie, Abou Diaby, Manuel Almunia, Denilson and Tomas Rosicky.

With Arsenal facing AC Milan in the last 16 of the Champions League on Wednesday, Wenger will not be taking any risks by selecting players who are not 100% fit.

But he assures United that the Gunners side he does pick will leave nothing in the locker room.

"We will fight, don't worry. We will dig deep tomorrow because we want to win the game and we want to qualify," he said.

"Man United are a big club and they will want to respond to their two disappointments they had recently (against Tottenham and Manchester City), so it promises to be interesting."

Arsenal sit five points clear at the top of the Premier League but Wenger, who has won the FA Cup four times, denies victory tomorrow will register a psychological blow in the title race.

"I feel United are still in contention. Two games ago we were second and that shows you how quickly it can change from one day to the next," he said.

"But it's always better to win because it makes you stronger. You want to win the big games because it makes your whole squad stronger."