Selling the players they currently have when their performance is declining will be a big loss for Manchester United, because the value of their players will also decrease. But keeping them is also not the right solution, Man United clearly needs a refresh in their squad. So whether they like it or not, Man United must sell their players at a loss and spend their money again to be able to recruit new players who are more promising.
Manchester united already made gross mistake when it comes to transfer market this season and it's already affecting their budget. Unless they correct the way they approach transfer market, it will continue to cost them heavily. Aside that Manchester united usually pay high for average players, they also hold on for so long when it comes to releasing their players at the appropriate time. Napoli came for Garnacho in January with a decent price but they turn the offer down.
PSG also offered a very good price for Rashford some years back but they rejected the offer and no team shows interest any longer and even if they do, the price will not be reasonable again as it was that time. Same thing is happening now regarding Bruno but they don't seem to have interest to release him. Unless they learn to release their players when a big offer comes, they will continue to be in financial constraints.