Leeds - England hooker Dylan Hartley's hopes of playing in the 2015 Rugby World Cup were left hanging by a thread after he was dropped from the hosts' training squad on Friday following his latest disciplinary problem.
The 29-year-old hooker - capped 66 times - was banned for four weeks on Wednesday after pleading guilty to headbutting Saracens' Jamie George during the second half of club side Northampton's Premiership semi-final defeat last weekend.
George has now replaced Hartley in England's squad.
New Zealand-born Hartley - who has now accrued 54 weeks in total of bans during his career - will miss England's three World Cup warm-up games and the tournament opener against Fiji at Twickenham on September 18.
Given the specialist nature of his position, England coach Stuart Lancaster said he had no choice but to ditch Hartley, although there remains the possibility he could yet be called up as an injury replacement.
"We are obviously very disappointed with the situation that Dylan has put himself in and where that leaves us as a squad," said Lancaster in a Rugby Football Union statement.
"I have spoken to him and he knows he has let himself and everyone down.
"If we selected him in the World Cup squad he would have played no competitive rugby at all and we would be left exposed with only two available hookers in what is a specialised position going into the Fiji game," Lancaster added.
"All it would take is one injury (that is not tournament ending) during the week of the Fiji game and we would only have one fit hooker in the squad for our crucial opening game and this would leave us massively exposed.
"In addition, the regulations also clearly state that in our World Cup squad we must have sufficient cover that is suitably trained and experienced in the front row in case of injury.
"This is clearly not the case if we begin the tournament with a suspended hooker and as such we have been left with no choice but to replace him.
"It also goes without saying that we need all our players to be able to control their discipline and make good decisions under pressure, the World Cup will clearly require this, and Dylan has not clearly displayed this in this latest incident.
"This is an area that he still needs to address.
"Dylan will be replaced by Jamie George in the World Cup squad and will not be considered until the suspension is served."
Earlier this month, Lancaster said Manu Tuilagi would not feature at the World Cup at at all after the England centre was banned after pleading guilty to assaulting a pair of female police officers.