The Red Devils are second in the Premier League though know victory will likely be needed in order to keep pace with leaders Manchester City, who face West Ham at home.
Mourinho has generally adopted a pragmatic approach in big away game games – he has not won away in any of his last 10 matches again rivals – but that could change against Arsenal.
Asked about his approach to the match, he said: ‘When we have the ball we are going to attack with 11 players – because even the goalkeeper needs to know what to do when we have the ball.
‘And when Arsenal has the ball we are going to defend with 11 players.’
Asked if that was pragmatic, he continued: ‘It depends what you think about risk.
‘In the beginning of football, the guy that decided to say “defenders” or “attackers”, this guy was bad.
Manchester United 2017/18 Fixtures
Arsenal (A) – Sat Dec 2
CSKA Moscow (H) – Tues Dec 5 (Champions League)
Manchester City (H) – Sun Dec 10
West Bromwich Albion (A) – Sun Dec 17
Bristol City (A) – Wed Dec 20 (EFL Cup)
Leicester City (A) – Sat Dec 23
Burnley (H) – Tues Dec 26
Southampton (H) – Sat Dec 30
Everton (A) – Mon Jan 1
Stoke City (H) – Sat Jan 20
Tottenham (A) – Wed Jan 31
‘Because in football everyone has to defend, everybody has to attack, especially in modern football.
‘So for me you can say what you want, you can analyse however you want.
‘My goalkeeper needs to know how to attack. My striker needs to know how to defend. My striker needs to know what to do when we don’t have the ball. For me it’s simple.’