The German international was left bleeding after a clash of heads with Scott McTominay during Sunday's 4-2 defeat to Manchester United.
After being bandaged and having his blood-stained shirt and shorts replaced, he played on before sitting down in the middle of the pitch a quarter of an hour later, then groggily walking off the pitch to be replaced by Junior Firpo.
"Leeds United can confirm that following a clash of heads, Robin Koch passed all of the on-field concussion screening tests that are currently part of the Premier League protocols," said a Leeds statement in response.
"The player was told if he developed any symptoms he should sit down on the field of play and would be substituted immediately, which is what Robin did in the 29th minute of the game.
"The medical staff at Leeds United have always been in favour of temporary substitutions for head injuries, as it would allow the staff more time to assess an injury and allow a period for symptoms to potentially develop.
"Robin will follow the concussion protocols before returning to play."
Koch tweeted on Monday: "Thank you for your many messages. I wanted to support the team for longer yesterday, but unfortunately I couldn't do it. Thanks to our medical staff for the good care. I feel much better today and will be back soon."
The complaint from the PFA, the players' union, is not that Koch played on with concussion, but that he played on with a suspicion of concussion.
The Football Association's concussion guidelines state: "Anyone with a suspected concussion must be IMMEDIATELY REMOVED FROM PLAY. Once safely removed from play they must not be returned to activity that day. Team-mates, coaches, match officials, team managers, administrators or parents who suspect someone may have concussion MUST do their best to ensure that they are removed from play in a safe manner."
It is the second such incident involving a Leeds player this calendar year. Firpo was allowed to play on after suffering an injury in the first half of their FA Cup tie against West Ham United which left him looking groggy, and was substituted in the second half complaining with blurred vision.
However, he was cleared to play against the same opponent seven days later in the Premier League.
Had he been deemed to have had concussion, he would not have been allowed to train or play again for a minimum of 14 days under the graduated return to play protocols.
The PFA is also unhappy that football has not followed the lead of other sports in allowing temporary concussion substitutes to allow for a proper assessment away from the field. Expert opinion is widely of the view that such assessments cannot properly be made within the space of a few minutes, as Koch's had to be.
Football teams are allowed an extra, fourth, substitute if a player comes off with concussion but once the injured player is substituted he cannot return to the game if he is found not to be concussed.