Van Nistelrooy will be in the visiting dugout tomorrow and, like Amorim, needs a win after a difficult run of results.
The East Midlands club have won just one of their last 10 league games and a cup run would provide some welcome respite.
The Dutchman is looking forward to returning to Old Trafford.
“It’s special to go back there,” he said. “I have history as a player, as an assistant, as a caretaker.”
Manchester United v Leicester team news
United will be without Lisandro Martinez and Luke Shaw.
Martinez suffered an ACL injury against Palace while Shaw has suffered a minor setback after a succession of niggling injuries.
January signings Patrick Dorgu and Ayden Heaven are both available.
Wilfred Ndidi has been declared fit for Leicester while Van Nistelrooy has confirmed 15-year-old Jeremy Monga and 17-year-old Jake Evans will be part of the squad.
Manchester United v Leicester expected line-ups
Manchester United: Onana; Yoro, Maguire, De Ligt, Dalot, Dorgu; Fernandes, Mainoo; Diallo, Garnacho, Hojlund
Leicester City: Hermansen; Coulibaly, Faes, Vestergaard, Kristiansen; Winks, Soumare, Ndidi; Ayew, De Cordova-Reid, Vardy
How to watch Manchester United v Leicester City: Live stream, TV channel
The game will be shown live on terrestrial television. ITV will screen it from 7.30pm UK time. The game kicks-off at 8pm.
Manchester United v Leicester City – the stats
- Manchester United have won their last 5 home matches in a row in the FA Cup while scoring more than 2.5 goals
- Manchester United have won 11 of their last 13 matches in the FA Cup while scoring more than 1.5 goals
- The last team to beat Manchester United in an FA Cup tie at Old Trafford in normal time was Arsenal in 2015
- In 3 of the last 4 Manchester United matches in the FA Cup, the total number of goals was over 6.5
- Leicester won the last FA Cup meeting between the sides, in 2021
- Leicester have lost 7 of their last 8 matches while scoring less than 1.5 goals
- Leicester have lost their last 5 away matches in a row while scoring less than 1.5 goals