Ben Thatcher has been suspended by Manchester City and charged by the Football Association following his challenge on Portsmouth's Pedro Mendes.
Mendes needed oxygen pitchside
Thatcher must answer a charge of serious foul play by 12 September.
And a statement on City's website said: "Ben Thatcher has been suspended from first-team action.
"This is pending the results of the club's internal investigation into the incident involving Pedro Mendes during the game with Portsmouth on Wednesday."
The statement continued: "The player will miss tomorrow's home fixture with Arsenal. Ben Thatcher fully agrees with this decision."
Thatcher was shown only a yellow card after knocking Mendes out with his arm.
But although referees are not allowed to retrospectively upgrade yellow cards, the FA said "the incident is being considered as an exceptional case".
"The FA contends that the challenge was sufficiently serious that had Thatcher been sent off, an additional sanction would have been merited."
Greater Manchester Police have also confirmed it had received complaints which it is "duty bound" to investigate.
Mendes needed oxygen at the pitchside and was later taken to hospital after Thatcher's arm propelled the Portuguese midfielder into advertising hoardings.
Manchester City have confirmed that Thatcher has written to Mendes to apologise for his actions.
Thatcher added: "Immediately after the game I tried to find out how Pedro was. I have written to him today apologising for what happened."
A statement on City's website said: "The club does not condone such action and the matter has been dealt with internally by manager Stuart Pearce."
The FA have to do something, it is there for all to see
Portsmouth boss Harry Redknapp
Greater Manchester Police will be talking to both clubs, Mendes and Thatcher.
A GMP statement added: "From those talks, GMP will decide whether any further action will be taken.
"There is no official criminal investigation but GMP is duty bound to investigate the complaints."
Pompey boss Harry Redknapp was incensed by the challenge and urged the FA to take retrospective action against Thatcher.
Redknapp said: "The FA have to do something, it is there for all to see.
The injured player can take civil action for carelessness or recklessness
"I do not want to see anyone suspended but how could that possibly not be a red card?
"What do you have to do to get a red, kill someone?"
Mendes travelled back to Portsmouth after overnight observation and a club statement said: "He will continue to be under medical and neurological supervision during the forthcoming week."
Meanwhile the chief executive of the Professional Footballers' Association has warned that Thatcher has left himself open to legal proceedings from Mendes.
Gordon Taylor said: "Players have a duty, which is a legal duty as well.
"In the eyes of the courts the referee has deemed it a foul and if it is considered reckless the player could have to pay a sum of money.
"Any contact with an elbow to the head has got be eradicated. It's not just football, it's the law of the land."
Specialist sports lawyer Mel Stein echoed Taylor's thoughts.
Stein said: "The injured player can take civil action for carelessness or recklessness.
"It's a bit like driving around Trafalgar Square at 100 miles per hour. You may not mean to cause harm, but are likely to do it."
Meanwhile, the PFA have offered to help Thatcher with any disciplinary problems he may have.
Taylor added: "The PFA has a duty to protect our members. We want to eradicate any reckless play that would endanger a fellow professional.
"I've known Ben since his time at Millwall. He's a robust defender who epitomises the physical side of football ,but that doesn't mean that someone like that is reckless."