Ireland prop Simon Best has been ruled out of the rest of the Rugby World Cup on medical grounds after being admitted to hospital last night.

Best has been transferred to a new hospital to continue tests after suffering from a loss of sensation down his right side last night.

Best, who has been ruled out of the World Cup as a result of his condition, was rushed to a Bordeaux hospital early yesterday evening after complaining of a mild headache and difficulty speaking.

The 29-year-old remained in hospital overnight and had several tests, including an MRI scan, an angiogram and a CT.

The tests were repeated this morning and Simon has been transferred to Haut Levque Hospital in Bordeaux for further investigation.

As yet doctors have been unable to give a clear diagnosis on his condition with an update expected later today.

Ireland coach Eddie O'Sullivan said: ``The thoughts of the management and all the players are with Simon at this time.

``He is an incredibly popular player and is a key member of the squad and it was a shock to everybody when we heard the news.''

Munster prop Tony Buckley has been called up to replace Best, who was named on the bench for Sunday's World Cup clash with Argentina in Paris.

Buckley will depart for France as soon as possible with Best's Ulster team-mate Bryan Young filling the vacancy on the bench against the Pumas.

A decision on who will start at hooker in the Pool D finale will be made later today with Rory Best (dislocated thumb) and Jerry Flannery (shoulder stinger) undergoing fitness tests.

Simon Best's condition may affect O'Sullivan's decision on who wears the number two jersey as Rory is the Ulster skipper's brother.

O'Sullivan admitted he is ``concerned'' by Best's condition but revealed brother Rory would train with the squad this afternoon.

The Ireland boss refused to speculate on what may be the problem, although Haut Leveque is one of France's main cardiological hospitals.

He said: ``We are concerned. There is a certain amount of concern because there isn't a diagnosis at this stage and I suppose that's the worrying thing.

``Rory's a bit upset with the news but he knows that Simon is in the best possible hands and that everything has been done for him.

``At this stage it's just a case of waiting to find what the problem is. I spoke to Rory at lunch and he's going to come training now.

``I wouldn't speculate on what Simon's condition is and I don't think anyone should speculate about it at this point in time. It would be wrong for everybody, including his family.

``We don't have a diagnosis and hopefully it's nothing like that (a stroke) - hopefully it might be something very, very small.

``In the meantime we have to keep our fingers crossed. The doctors won't speculate. He has been moved for further investigation and the medics won't speculate.

``I'm sure they may have opinions, but you can't expect them to speculate on these things.''

O'Sullivan was visibly shaken by the latest development in Ireland's disappointing World Cup, admitting it had come as a shock to the whole camp.

He said: ``Simon has been around for a long time and he's one of these quietly-spoken guys that everybody loves.

``So it's a shock for everybody that something like this can happen.

``Simon was in downtown Bordeaux yesterday afternoon with his good friend Paddy Wallace, just strolling around the city centre, when he felt this coming on.

``He called our team doctor (Gary O'Driscoll), we got him back to our hotel immediately and then we moved him to the hospital straight away. He's been in
hospital since.

``Simon's wife is en route here at the moment. His dad will be here tomorrow. He will be going home at some stage so obviously, we want family travelling with him.

``We have an issue that we didn't expect to have with one of our friends, one of our family. We have to get on with our preparation because the game is going to go ahead regardless.

``It's just about getting that balance right in our heads. We're training this afternoon so we've to go out and get that part of the job done.

``Hopefully, when we come back from training we'll have better news from the hospital.

``There's no timeframe. Gary O'Driscoll has been with him since this happened and he's keeping us update.

``But now that he's moved hospital I suspect that there won't be any news until they've done further tests. That could take a number of hours, I don't know.''