His resignation from the Irish team comes after he believed he had been selected to compete in Friday’s Nations Cup in Dublin, only to find out an hour later he was not one of the four riders chosen.

Mr Marshall has blamed the army and Cian O’Connor for putting pressure on the chef d’equipe Eamon Rice – who selects which riders from the team will jump in the competition – to choose Capt Shane Carey above him.

In a statement issued today the EFI said: “It is not the responsibility of the individual riders to decide who does, or does not, jump on any of the senior teams.

“Nor is it proper for a rider to withdraw their name from possible future selection if they are unhappy that they themselves were not selected for a particular team.

“This type of behaviour would make the sport ungovernable were it allowed to continue.”

Mr Marshall said he was already uncomfortable about riding with Mr O’Connor before last week’s competition.

He has now taken a stand alongside colleague Jessica Kurten, who has refused to compete with Cian O’Connor since he was stripped of his gold medal during an arbitration hearing.

Mr Marshall said the mood in the team had been poisonous since Mr O’Connor returned to the national squad after serving a three-month ban for inadvertently giving his horse a banned substance.

“I’ve been on two Nations Cups with him so far and the atmosphere has been appalling.

“I wouldn’t want to be there again, I don’t need that.”

“I would not jump in another team with Cian O’Connor,” he told RTE Radio.

But Colin McClelland, spokesman for the EFI, said most people in the sport were happy to jump with Cian O’Connor.

“It’s not like there is a major split in Irish showjumping, it’s a small number of people.

“But we don’t approve of it and we need everybody in the team to pull together,” he said.

The Irish team are in second-to-last place in the Samsung Super League after finishing fifth in the Aga Khan trophy in Dublin last week, and face relegation from showjumping’s top division.

The sport was thrown into further crisis last night when two of the selectors on the International Affairs Committee of the Show Jumping Association of Ireland walked out of a meeting during a discussion over what had happened in Thursday’s selection process.

It appears Mr Rice asked Mr Marshall on Thursday at 6pm whether he would be happy to jump first in the order, leading the showjumper to believe he had been selected, before finding out at 7pm he was not.

Today chairman of the selectors committee Taylor Vard said it was up to the chef d’equipe to select the team and he did not know what had made him change his mind.

“We’re going through a difficult situation, we are second last in the Super League and we need everybody to pull together.

“If there are arguments, if there were mistakes made, we should be sitting round a table discussing them, not airing them on radio, papers or TV,” he told RTE Radio.

Mr Vard said the selectors had every reason to bring Cian O’Connor back into the squad, as he had served his ban and only two members of the Irish team objected to his presence.s