Nico Yennaris suffered a serious injury in the closing stages of the first half of Brentford's game with Preston.
The midfielder was accidentally caught in the face by Jordan Hugill which knocked the former Arsenal man out as the North End man looked to charge down the Bees' kick off after Sean Maguire's goal.
Yennaris was treated on the pitch for nine minutes, by both sets of medical teams, and stretchered off.
The 24-year-old had opened the scoring before Maguire levelled it up moments before the blow from Hugill.
An update on his condition will be provided as soon as possible. It is the second time this season a Brentford player has been knocked out with Henrik Dalsgaard suffering a blow against Sheffield Wednesday.
