I have played in a back three at Man United and it will be difficult for Ruben Amorim to implement

It will be difficult for Ruben Amorim to introduce his favoured 3-4-3 formation to Manchester United midway through the season.

That is the frank verdict of former United defender Phil Jones, who played in a back three under Louis van Gaal at Old Trafford.

Amorim will become United's new permanent manager on Monday, November 11, with Ruud van Nistelrooy remaining in interim charge for this week's games against PAOK and Leicester City.

READ MORE: I played alongside Bruno Fernandes at Man United - he is misinterpreted and an excellent captain

READ MORE: Casemiro shows true colours with verbal warning for Manchester United youngster Alejandro Garnacho

Under van Nistelrooy, and previous manager Erik ten Hag, United have played with a 4-3-3/4-2-3-1 formation but Amorim has enjoyed great success in Portugal with his 3-4-3 formation.

He has twice guided Sporting CP to the Portuguese Primeira Liga title and his philosophy was one of the big attractions for United in appointing the 39-year-old as their new head coach.

However, Jones, who was working as a pundit on Match of the Day 2 following United's 1-1 draw with Chelsea on Sunday, has warned it will take time to introduce his favoured 3-4-3 formation to a defence that is used to playing as a back four.

"No, that takes practice on the pitch," Jones replied when asked if it would be easy to introduce a new system midway through the season.

"We played a back three under Louis van Gaal and spent many hours on the pitch getting the distances right. I always think the two centre-halves on the outside of the middle one, when the wing-back jumps, you have big spaces to cover.

"The timings of the actions have to be spot on. It will be difficult and it is a difficult job but listen