The Newcastle United defender was knocked out against Georgia at the weekend – but cleared to play on after treatment.
Schar went on to have a hand in both Switzerland goals in Saturday’s Euro 2020 qualifier in Tiblisi.
The 27-year-old wanted to play against Denmark in tonight’s qualifier in Basel.
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“As you probably know, I will not be allowed to play,” said Schar in an Instagram post.
“I really wanted to play, and, as always, give everything to the team and Switzerland, but unfortunately this time the decision is not in my hands, but was imposed on me by FIFA for health reasons.
“In the game against Georgia, I was unconscious for a short time after a collision.
“Anyone who knows me knows how I feel and how much I would like to play.
“Of course, I keep my fingers crossed for the team and I’m convinced that we will have a good game.”
The decision to allow Schar to stay on the pitch has led to a call for a UEFA investigation into the incident.
In the Premier League, a player must be taken off if there is a confirmed or suspected loss of consciousness.
There are also Football Association and Premier League guidelines which set out how quickly a player can return for a club.
Speaking after the game, Schar said: “It looks awful. I can’t remember anything.
“I was out for a few seconds. My skull is still humming, and I’ve got neck ache and a bruise on my forehead, but it was worth it.”
Those “disturbing” comments shocked Peter McCabe, the chief executive of brain injury charity Headway.
“Put simply, the decision to allow Fabian Schar to return to the field of play after suffering a clear concussion was not only incredibly dangerous, but also a clear dereliction of duty,” said McCabe.
“The player’s comments after the match are also deeply disturbing, and again show the lack of awareness and understanding among players.
“UEFA must immediately launch an investigation into the incident and explain why their protocols were not followed.”
Schar – who is suspended for Newcastle’s April 1 game against Arsenal at the Emirates Stadium after picking up 10 club bookings – yesterday left Switzerland’s training camp, though he will watch the Denmark game before returning to Tyneside.
Switzerland team doctor Damian Meli said: “Returning after such a collision takes some time.
“It usually takes a few days, a time that is missing between the two games against Georgia and Denmark.”
The decision to withdraw Schar was taken jointly by Newcastle and Switzerland after footage of the incident was reviewed.