Wales captain Gareth Thomas will miss the rest of this season's RBS 6 Nations Championship after suffering damage to an artery in his neck.

The Toulouse star faces up to 12 weeks out, having undergone an MRI scan after going to hospital on Sunday night suffering from a severe migraine.

Number eight Michael Owen replaces Thomas as skipper against Ireland in Dublin next Sunday, with Llanelli Scarlets' Lee Byrne taking over at full-back.

Thomas could conceivably be sidelined for the rest of this term, also dealing Heineken Cup quarter-finalists Toulouse a major blow.

He had hoped to travel to Dublin with his Wales team-mates, but rest has now been advised and he will remain at home.

"Gareth Thomas has sustained damage to an artery in his neck," said Wales team doctor, Professor John Williams.

"This caused the symptoms that he experienced on Sunday night and resulted in his admission to hospital.

Those symptoms have since resolved. He has undergone detailed investigations and has been reviewed by a consultant neurologist at the University Hospital of Wales.

"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 appeared on a BBC Wales television programme on Sunday night, when he was grilled for 30 minutes about Mike Ruddock's shock departure as Wales head coach. He complained of feeling unwell shortly afterwards.

Caretaker coach Scott Johnson added: "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.

"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. We wish him a speedy recovery and hope to have him back with us soon."