The Scottish midfielder collapsed on the field in the second half, without a Reading player around him, and was taken to hospital after lengthy treatment on the pitch.
He was able to stand, with an oxygen mask on, and United confirmed he was conscious when he was taken to hospital by ambulance.
Here’s how we rated United’s players on an evening when the result seemed somewhat secondary...
5. Ben Davies 7
Was in the right place at the right time to cut out Yiadom's dangerous cross as Reading mounted their first real attack of the game. Stood up well to the aerial threat posed by Carroll Photo: Simon Bellis
6. Enda Stevens 6.5
Solid rather than spectacular, Stevens' best contribution all night may well prove to be the first help he gave to Fleck after his teammate went down on the turf after suffering a medical emergency Photo: Simon Bellis
7. Ollie Norwood 7
Back in the side after his suspension against Coventry, his delivery from deep caused some problems for Reading early on and he was good on the ball throughout, doing his share off it too. United look better with him in midfield Photo: Simon Bellis
8. John Fleck n/a
Took a booking for the team after losing his footing in midfield and dragging down Ejaria as he looked to take advantage and race away. Left the field on a stretcher after a concerning medical episode in the second half. Get well soon, John Photo: Simon Bellis