Sancho agreed personal terms with United before the club had a £72.9million bid accepted by Borussia Dortmund three weeks ago and the 21-year-old arrived at United's Carrington training complex last week to complete a medical.
United had planned on confirming the Sancho deal late last week but there has been a hold-up in finalising the paperwork. Sources are hopeful the signing will be announced before the weekend.
United manager Ole Gunnar Solskjaer said there were 'small details' to address before the club could parade Sancho.
“From what I understand only paperwork, small little details, hopefully we can announce something," Solskjaer said after United's pre-season friendly win at Derby on Sunday. "Let's get all the paperwork done and get him over the line and then I can say what I truly feel about the player."