Alex boss Steve Davis believes the England Under-18 international's representative is currently negotiating over a move away from Gresty Road and it is understood United head a group of clubs expressing an interest.
"Nick is still with us, but I am sure talks are still ongoing with his agent and clubs," Davis told Crewe's official website.
"These things take time and rightly so because all parties have to be satisfied with any deal.
"I still envisage him leaving us this summer, but if it doesn't happen then we would welcome him back for pre-season.
"We'll see what happens this week because obviously I would like to know as soon as possible if we are moving forward without him or not."
The move away from Crewe would be final for Powell, with Davis ruling out the prospect of an immediate loan return being part of any transfer deal.
He added: "One thing I can confirm is that he won't be coming back here on loan.
"That wouldn't be part of it because we want to bring in a replacement of our own and give our own players, such as (fellow England Under-18 forward) Max Clayton, a chance."
Last season proved to be a breakthrough campaign for Powell, who picked up Crewe's player of the season award after scoring 16 goals in 45 appearances.
The 18-year-old further enhanced his reputation with a spectacular strike to open the scoring in last month's 2-0 League Two play-off final victory over Cheltenham at Wembley.