In a surprise tweet on Tuesday night, the striker simply replied "Yes x" to a fan asking for him to "announce Sancho Marcus".
United are understood to be closing in on Sancho's signature after failing to land the fellow England international last summer.
A deal worth around £80million is expected to be completed after United met Borussia Dortmund's asking price, which was around £30m less than last year.
The news will be met with joy and relief from United fans with the transfer over a year in the making.
How United or, more importantly, Dortmund will meet the impromptu announcement remains to be seen, however.
Both Rashford and Sancho were at Wembley on Tuesday as England beat Germany to reach the Euro 2020 quarter-finals.
Raheem Sterling and Harry Kane scored as the Three Lions set at Saturday date with Ukraine in Rome.