Ben Thatcher has apologised for the horror challenge which could land him in trouble with the police as well as the Football Association.

Thatcher has sent a letter to Pedro Mendes expressing his regret at the incident which saw the Portsmouth midfielder knocked unconscious at Eastlands last night.

Mendes suffered a seizure and required oxygen before being taken to a local hospital after being struck in the face by Thatcher's forearm.

Although the 27-year-old has now been released, he will required medical and neurological supervision over the next week before he is cleared to play again.

"Immediately after the game I tried to find out how Pedro was," Thatcher told www.mcfc.co.uk.

"I have written to him apologising for what happened."

Leading figures within the game were quick to condemn Thatcher, with TV pundit Gary Lineker labelling the tackle "shockingly dangerous".

Portsmouth boss Harry Redknapp was equally damning and while City counterpart Stuart Pearce initially suggested referee Dermot Gallagher had been correct to dish out a yellow card, after reviewing the incident again both he and Blues chief executive Alistair Mackintosh have felt compelled to take action.

"Chief executive Alistair Mackintosh has telephoned Portsmouth's chief executive Peter Storrie to enquire about Pedro's health," said a City statement. "The two clubs share an excellent relationship and everyone at Manchester City, especially Ben himself, wishes him the very best.

"The club does not condone such action and the matter has been dealt with internally by Stuart Pearce."

While City are refusing to elaborate on the disciplinary action Thatcher has been subjected to, it seems certain the Welsh international has been heavily fined. Whether that will be enough to dissuade the Football Association from launching a charge against the 30-year-old remains to be seen.

Ordinarily, Gallagher's decision to yellow-card 30-year-old Thatcher would have marked the end of any disciplinary action by the FA. However, Soho Square officials are already looking at the possibility of charging the full-back.

If that was not bad enough, Thatcher has been warned by Professional Footballers' Association chief executive Gordon Taylor that he has left himself open to a law suit, should Mendes opt to pursue the matter.

Greater Manchester Police are also investigating a number of complaints.

"Players have a duty, which is a legal duty as well," said Taylor. "In the eyes of the courts the referee has deemed it a foul and if is it considered reckless the player could have to pay a sum of money.

"Any contact with an elbow to the head has got to be eradicated - it's not just football, it's the law of the land."

It is not the first time Thatcher has found himself in trouble for reckless behaviour. Six years ago, he was banned for three matches by the FA after being caught smashing his elbow into the face of Nicky Summerbee.

And earlier this month, on the Blues' pre-season tour of China, the former Tottenham defender was sent off against Shanghai for two bookable offences. He left an opponent requiring hospital treatment for a punctured lung after a similar challenge to last night's, which also went unseen by the referee.

West Ham manager Alan Pardew believes the FA need to take retrospective action.

He said: "Serious incidents, which I think you have to class that one as, perhaps do deserve to have special dispensation in terms of looking at it. If I was the manager of the player who was the victim in that case I would have been very, very upset. I think everyone in football, including Ben Thatcher, doesn't want to see those incidents.

"They happen occasionally. Perhaps it is a situation where it should be marked and say 'we can't accept it'."