Paul Gallagher is a doubt for Preston North End's Deepdale clash with Reading on Saturday after getting a bang on the head in the defeat to Derby County.
Gallagher was hurt within a few minutes of coming on as a second-half substitute at Pride Park but completed the game.
He went to hospital after the game having complained of feeling unwell.
Speaking at his pre-match press conference at Springfields on Thursday morning, PNE boss Alex Neil said: "Gally is off today, needs to recover from that head knock, we think he has a bit of concussion, a bit of whip lash which is not great.
"Having spoken to Paul, we think he actually got it within five minutes of coming on but no one realised.
"He has got no recollection of the game so I just told him when he came on he did very well!
"Gally felt sick after the game, we got to the doctor to him and then took him to hospital.
"We did all the procedures which are necessary.
"Anything around the temple or behind the ear - he got the knock behind his ear - you have to get it checked out."
Greg Cunningham is another fitness concern for the Reading game, the skipper having hyper-extended his right knee in the latter stages at Derby.
Neil said: "Hopefully Greg will be okay although it is probably too early to tell at the moment.
"We will see how he develops over the next 24-48 hours."
Cunningham, 26, was subject of a bid from Cardiff on Tuesday, one which North End swiftly turned down.
Neil said: "There is interest but Cardiff City have been told under no circumstances would we be interested in selling Greg Cunningham."