Wales captain Gareth Thomas will miss the rest of the Six Nations

Thomas was taken to hospital on Sunday with a severe headache, but a scan on Tuesday revealed the neck injury.

"This caused the symptoms that he experienced on Sunday night and resulted in his admission to hospital," said Wales team doctor John Williams

He is expected to make a full recovery and resume training in 10-12 weeks, but may well miss the rest of the season.

The cause of the artery problem remains unclear, although it appears that restricted blood flow to the head was responsible for Thomas' extreme discomfort on Sunday night.

Thomas was first taken to hospital on following his appearance on the BBC Wales Scrum V programme on Sunday, when he defended the actions of his players in the run-up to former coach Mike Ruddock's dramatic departure.

We should be smart and distinguish between the current farce and this health problem and wish him well From F Have your say on Scrum V

The Wales captain, who went to hospital after taking a blow to the head playing for Toulouse against Pau three weeks ago, spoke of not having slept for five nights due to the worry of the Ruddock situation.

It was first thought that stress had caused a severe migraine, the diagnosis when the Toulouse player was rushed to hospital after losing feeling in the left side of his body.

"I thought I was having a heart attack. I thought I was going to die," Thomas said after his first visit to hospital.

"I was looking around the room at my family thinking, 'This is the last time I am going to see you all.'

"It has reminded me that my health and my family must always come first."

The damaged blood vessel now needs to be given time to heal Wales team doctor John Williams

However, Williams is sure that Thomas is already on the road to recovery.

"Those symptoms have since resolved," the Wales team doctor said.

"He has undergone detailed investigations and has been reviewed by a consultant neurologist at the University Hospital of Wales today (Tuesday).

"The damaged blood vessel now needs to be given time to heal before Gareth can resume training and eventually playing.

"We are expecting him to make a full recovery and it is envisaged that he will be able to resume training after 10 to 12 weeks."

Thomas feared he was going to die

Caretaker Wales head coach Scott Johnson has not named Thomas in the team to play Ireland on Sunday.

Johnson had been hoping his inspirational captain could travel with the squad to Dublin and play a leadership role within the team, but Thomas will now not make the trip.

"We need to do what is in the best interests of Gareth Thomas in this situation, listen to the doctors' advice and leave him at home to rest," said Johnson.

"We will all be thinking of him, but his personal health is of a much higher priority to us all than anything that can happen on a rugby pitch.