Unai Emery hopes the return of Rob Holding will put an end to his Arsenal side being the defensive laughing stock of the Premier League.
Holding, only 24 last week and a surprise omission from Emery's five-strong captain leadership group, is the key.
The Spanish coach confirmed: 'When he suffered his injury at Old Trafford he was maybe at the best moment [in his career].
'To then have nine months out it takes a long time to recover. First he had to find his fitness, confidence and then match the demands for our performance. He has progressed a lot since he started training and playing with us..'
Holding's first steps to a full first team return came in Tuesday's 5-0 League Cup drubbing of Championship promotion hopefuls Nottingham Forest.
'When I saw him on Tuesday I thought 'wow!' He's coming back - Rob Holding!
'I can not be certain he will start on Monday but I want him there for his spirit, his behaviour, his commitment.
'He feels really Arsenal Football Club and I want players like him in the dressing room.'
That will put pressure on either error-prone David Luiz or Sokratis in a match between two fading Premier League giants, but a fixture Emery regards as one of the biggest in world football.
He explained: 'It was always as special moment when I watched in Spain, Arsenal-Manchester United, Manchester United-Arsenal. I think Monday at eight o'clock, in all the world, if someone wants to watch a football match, it will be this one.'
Emery's United debut as Arsenal boss ended in a 2-2 draw last season and he added: 'It's amazing to play in Manchester with that atmosphere.
'We really want to play matches where we can do something important. We know it's a very big opportunity for us to get three points.
'I am excited waiting for this moment. But also I know we need to prepare a perfect match because three points is very important for both sides.'
To achieve that and boost Arsenal's top four hopes, Emery will have to outwit United manager Ole Gunnar Solskjaer, another coach struggling to convince fans and pundits alike he is the right man for the job.
'In 38 matches you are going to try to be consistent and sometimes there are matches against a rival with the same objective. It's a very good moment.
'Solskjaer has experience. He was a player at Manchester United, he knows the club perfectly, he knows the high competition, the high level and he now has very good players.
'His challenge is also to achieve the consistency and performances that will get them in the top four. We are going to fight on Monday for the first time this season and it's about which team can respond.'