Mills has told Sancho there would be 'no point' in completing a move to United if they miss out on the Champions League.
He told talkSPORT: “If I was Jadon Sancho I'd be wanting to ask the questions: “Who else are you bringing in? What other signings have you got lined up? What is the squad going to look like next season? Are you realistically going to be challenging for things? Who is going to be the manager… is it still going to be Ole Gunnar Solskjaer next?
“He's in a position of strength at the moment. He wants to go and win things, that's the most important thing.
“He's going from a fantastic club, he's gone through his development phase, he's now going to start hitting the peak development phase and he wants that to be the best years.
“There's no point going to Manchester United next season if they're going to finish sixth or seventh."