The 20-year-old joins the West Country outfit on a two-year deal, as The Glovers prepare for their maiden season in League One.
The youngster impressed Huish Park boss Gary Johnson during an end-of-season trial, having struggled to make a break into United's first team plans.
"David is a great capture for us," said Johnson.
"Manchester United obviously thought he could be a Premiership player, so he has great potential."
?????????? And they released him?