The 20-year-old ace - who left local rivals Manchester City for Borussia Dortmund three years ago - is said to have agreed on almost all details regarding a potential move.
According to SunSport, the England star has held secret talks with the Red Devils, meaning specifics like contract length, salary, bonuses and a big buyout clause have all been figured out.
Although Chelsea are also interested in Sancho, it's said he's very keen on joining Ole Gunnar Solskjaer's side.
It's now down to the clubs to finalise a fee, and Dortmund will want what would be a record fee for a British club - eclipsing the £89 million United paid to sign former academy prospect Paul Pogba from Juventus back in 2016.
United first made contact last summer, and the London-born attacker is reportedly keen on a switch back to the Premier League.
Back in September, Dortmund chief Michael Zorc confirmed: "A meeting did take place. United invited the agent."
Meanwhile, United chief Ed Woodward is also looking to back Solskjaer further in the transfer market with an additional move for Aston Villa midfiler Jack Grealish, and he could test Spurs' resolve over a deal for superstar striker Harry Kane.