Wales' team doctor has allayed fears over the fractured skull centre Jamie Roberts suffered against Australia.
Professor John Williams said: "I've never seen anything like this... some of my colleagues...have never seen anything like this.
"It's an undisplaced fracture so it means that it is a crack which hasn't moved so it hasn't caused any internal damage to the brain.
"It is a clean fracture which should heal very easily."
Medical student Roberts played a major part Shane Williams' opening try in the fourth minute of their 21-18 win over the Wallabies at the Millennium Stadium.
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Mortlock departed after receiving treatment, but the Cardiff Blues centre played on until the injury took its toll.
Williams added: "It is a fracture extending back from above the nose along the roof of the eye towards the central structures in the base of the skull.
"He was admitted to hospital last night (Saturday) with a fracture to his skull. He is comfortable, pain free. He will be out of training for six weeks to give it a chance to heal and then back in the New Year.
"After the contact Stirling Mortlock looked like he had come off worse.
"Jamie was conscious throughout and there were no signs of anything, no suggestion of a fracture or any problem with his nose or eyes. The contact was with his forehead.
"And then the headache gradually came on... and we pulled him off as the headache got worse.
"He is a pretty tough guy - it's a very unusual injury.
"It was a collision of heads at a certain angle with a certain momentum causing a crack.
"The second week of January he could be back in contact which is three weeks before the Six Nations. We will just watch over the next two or three weeks while this heals."
Williams revealed Roberts' team-mates were thankful for his efforts, saying: "He (Roberts) texted the team (from the hospital) and the team thanked him for taking Stirling Mortlock out of the game!"
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