The centre-back clashed heads with Belgium forward Jassina Blom in the 19th minute in a nasty collision.
Greenwood was treated on the pitch for almost 12 minutes by four members of England’s staff and six medical personnel.
The defender was eventually carried off on a stretcher while receiving oxygen and at half-time she was understood to be conscious and talking and being monitored by medical staff.
Wiegman later confirmed that Greenwood was up and walking and was "doing fine", having suffered a suspected concussion.
England were trailing 1-0 at that point following Laura De Neve’s opener and they responded well, even taking the lead through goals by Lucy Bronze and Fran Kirby.
But they were far too vulnerable to the counter-attack all night and were eventually made to pay. Tessa Wullaert struck twice and England shipped three goals for the first time under Wiegman to lose 3-2.
It leaves the Lionesses’ hopes of securing qualification for Team GB at next summer’s Olympics hanging by a thread.
They are now third in Group A1 and trail leaders the Netherlands by three points, with the two sides due to meet at Wembley in December.
England must win that game and they will believe that they can, especially given the memorable moments they have had at Wembley in the past.
They showed flashes of the brilliance of old here in Leuven, not least with their two goals before half-time.
First, Bronze expertly headed home Chloe Kelly’s free-kick and then Kirby marked her first start for the Lionesses in 385 days by scoring.
Kirby finished off a flowing move, which began with Keira Walsh’s diagonal pass picking out Lauren Hemp. From there, Hemp skipped past her opposite number and teed up Kirby to score with a brilliant back-heel.
That felt like the spark England needed and they enjoyed a period of dominance after that where they could have killed the game.
Instead, though, they were punished. Belgium hit back before the break as Wullaert scored after England gave the ball away in midfield.
Wullaert was a thorn in the Lionesses’ side all night and only a fine save from Mary Earps stopped her scoring initially in the second half.
She was not to be denied, though, and five minutes from time she slotted the winning penalty after Georgia Stanway’s handball.