Eric Garcia was taken off on a stretcher after a sickening collision with Ederson during Manchester City's clash with Arsenal.
Pep Guardiola's side were already 2-0 ahead thanks to goals from Raheem Sterling and a Kevin de Bruyne penalty, with both strikes handed to them by two costly mistakes from David Luiz, who was subsequently sent off.
However, there was a sour note for Manchester City as Garcia collided with Ederson after the goalkeeper came racing out of his goal to clear a ball.
With Garcia smashed to the ground, both clubs' medics raced on and treated the 19-year-old for 10 minutes before he was taken off, leaving City to play the final minutes with 10 men.
City players surrounded Garcia and medical staff spent more than five minutes with the 19-year-old assessing him and then moving him onto a stretcher in what was a sombre way to end what had been a comfortable evening on the pitch for the hosts.
Manager Pep Guardiola was told by the doctor that the player was conscious before going off to hospital.
"We are concerned about Eric of course. He is conscious but I think he is going to be tested tonight because a kick in the head is always so dangerous," he said.
"The doctor told me he was conscious and they asked me to be with you. I'm pretty sure we're going to do absolutely everything to be sure that everything is fine and well."
Players from both sides gathered around with concerned looks on their faces while Garcia was treated before the player was eventually stretchered off the pitch, having started the match alongside Aymeric Laporte and ahead of Nicolas Otamendi.
It was a tough night for injuries at the Etihad Stadium, with Arsenal losing Pablo Mari and Granit Xahaka inside the opening 25 minutes, which saw Luiz enter the fray.
He endured a night to forget though, first allowing de Bruyne's pass to find Sterling for the opener, before hauling down Riyad Mahrez which allowed the Belgian to double the lead.
After the match restarted Phil Foden added a third to provide further breathing room for City in a dominant display.