The 18-year-old will play no part for Aidy Boothroyd’s side in upcoming fixtures against Slovenia and Austria after he was forced to return to Old Trafford after picking up a back complaint.
Greenwood did manage to make it off the bench for United in their latest Premier League outing, as he was introduced by Ole Gunnar Solskjaer during their 1-0 defeat to Newcastle.
The hope was that he would get further minutes under his belt during the international break.
Greenwood currently has two U21 caps to his name, but will now spend the next two weeks with his club.
United will be hoping that an untimely knock is not too serious as their next game is set to see them play host to arch-rivals Liverpool.
A statement released by the club said of Greenwood: “He will remain at the Aon Training Complex in advance of the Reds' next outing, against Liverpool at Old Trafford on Sunday, October 20.”
The Red Devils already have a number of walking wounded within their ranks.
Paul Pogba continues to struggle with an ankle issue, while fellow Frenchman Anthony Martial is nursing a thigh complaint.
Jesse Lingard has a similar ailment and Phil Jones, Eric Bailly, Victor Lindelof, Diogo Dalot, Timothy Fosu-Mensah and Aaron Wan-Bissaka have all been missing from the defensive ranks.
Greenwood has now been added to the list, with England’s U21 side seeing three players removed from the reckoning.
After seeing his ranks depleted, Boothroyd has called upon Swansea duo Sam Sturridge and Ben Wilmot.
“For striker Surridge, it’s a first England call-up at any level while defender Wilmot was involved in last month’s squad as the Young Lions started their new U21 Euro qualifying campaign with victories over Turkey and Kosovo.
“The U21s squad will train at St. George’s Park until Thursday when they head to Maribor for Friday’s game with Slovenia.
“It’s then back to Milton Keynes for their next qualifying game with Austria at stadiummk.”
As the Young Lions finalise their plans, at senior level Gareth Southgate will be without Fabian Delph for Euro 2020 qualifiers against the Czech Republic and Bulgaria after seeing the Everton midfielder ruled out of his plans.
No replacement has been called up.