The Reds drafted in Aaron Wan-Bissaka, Daniel James and Harry Maguire during the summer, but that is nowhere near enough as they have got off to a disappointing start to the season.
Pundits and former players have suggested several transfer windows will be needed to get the United squad where it needs to be, and upwards of £700million will need to be spent on it. United's recruitment has been criticised recently although the addition of Rice and Koulibaly would be seen as good business if they can be snapped up.
That will be easier said than done, but reports are suggesting both players are high on the club's wanted list and attempts will be made to get them on board at the end of the campaign.
Central midfield and defence are areas that need strengthening and Rice and Koulibaly are two of the best out there in those positions.
Rice has spring to prominence over the last 12 months following some fine performances for West Ham, which have led to him being called up into Gareth Southgate's England squad.
The player has insisted he is happy at West Ham and is not pushing for a move, but his head would no doubt be turned if United made a firm offer.
The same could be said of Koulibaly, the powerhouse central defender, who would be the perfect partner for Maguire.
Napoli are also ambitious and have so far managed to keep hold, but they could be open to a sale if things do not go according to plan this season.
United would need to break the bank to get both and that is exactly what is required if they are to challenge for top honours once again.