Sir Alex’s men beat Fulham 4-1 on Saturday afternoon at Old Trafford, while Reading progressed following a 4-0 home win over Sheffield United.
The two sides have met 12 times before in the FA Cup and will do so again on the weekend of 16/17 February (date and kick-off to be confirmed).
United have lost just one of those previous 12 meetings, winning six and drawing five.
FA Cup fifth round
Huddersfield/Leicester v Wigan Athletic
MK Dons v Barnsley
Oldham v Everton
Luton v Millwall
Arsenal v Blackburn
Man City v Leeds
United v Reading
Middlesbrough v Brentford or Chelsea
Ties to be played Saturday 16 or Sunday 17 February.