Simon Best, the Ireland prop, will return home this weekend after his collapse here on Wednesday, which doctors believe was heart related. Best’s World Cup ended when he was rushed to hospital complaining of a loss of sensation down his right side, a headache and difficulty speaking. At first it was thought he could have suffered a stroke, but further extensive tests at a specialist clinic yesterday ruled out neurological problems.

As the Ireland squad departed for Paris last night, before their crucial final pool D game against Argentina on Sunday, Best remained in hospital, where his condition was described as comfortable. He was joined by Katy, his wife. John, his father, is due to arrive today.

Best, 29, was a passenger in a car being driven by Paddy Wallace, his Ulster teammate, when he was taken ill. The player, whose younger brother, Rory, is one of Ireland’s hookers at the tournament, had been named on the bench to face the Pumas at the Parc des Princes on Sunday, the match that will decide Ireland’s fate. He won the most recent of his 23 caps as a replacement in the 25-3 defeat by France a week ago.

Gary O’Driscoll, Ireland’s team doctor, has been with Best since he was admitted to hospital, where he underwent an MRI scan, an angiogram and a CT scan. He was transferred to a cardiological unit yesterday, where further investigations suggested a more optimistic prognosis. “This is very positive news for Simon and we will all continue to monitor his progress carefully,” Eddie O’Sullivan, the Ireland coach, said. “The care he has received so far has been excellent.” Best’s illness is the latest setback to befall Ireland’s troubled campaign in France. They need to win Sunday’s match, score at least four tries to earn a bonus point and deny Argentina a bonus point if they are to progress to the quarter-finals – unless Georgia beat France.

However, Best’s plight dominated thoughts yesterday. “He is a hugely popular player and a key member of the squad and it was a shock to everybody when we heard the news,” O’Sullivan said. “We have a match on our hands, which of course we will try to get on with, but Simon is the priority at the moment.”

The Belfast Harlequins prop, who captained Ireland on their summer tour to Argentina, will be replaced by Tony Buckley, of Munster, who has two caps. Bryan Young, of Ulster, comes on to the bench. Both Jerry Flannery (shoulder) and Rory Best (dislocated thumb) passed fitness tests yesterday, with Flannery starting at hooker and Best among the replacements.

“We did consider his brother Simon’s condition when making that decision,” O’Sullivan said. “But Rory is an incredibly mentally tough individual and was adamant that he wanted to be considered for selection. We have no doubts that he will be ready if called upon.”

Argentina name their side today, with Felipe Contepomi, the centre who plays for Leinster, confident that the Pumas will not wilt as they seek a place in the last eight for the first time, against either Scotland or Italy.

“The first thing for us is playing as we always do and try to keep possession of the ball,” Contepomi said. “The less they have the ball, the fewer tries they can score. I expect our defence to work as it did until now, being the only the team unbeaten in the pool.”

Taking its toll:

Players who have had to leave the World Cup

Jamie Noon (England centre): knee injury

Mark Gerrard (Australia wing): torn medial ligament

Jean de Villiers (South Africa centre): torn left bicep

Takamichi Sasaki (Japan flanker): knee ligament strain

Yuki Yatomi (Japan scrum half): ankle injury

Allan Jacobsen (Scotland prop): torn left calf

Marcello d’Orey (Portugal lock): calf injury

Luke Gross (US lock): burst disc

Ilia Zedginidze (Georgia lock): broken knee cap