Injury has ruled out Gavin Henson and nothing else says coach Warren Gatland

The head coach conceded that he had "no idea" when Henson would be fit after a scan was ordered on the troublesome Achilles tendon which had forced him to withdraw from the team to play South Africa last Saturday.

Gatland said the comments on Friday of assistant coach Rob Howley that Henson was not "mentally and physically ready" to play against South Africa had been taken out of context.

"I've got no idea when he will be fit. We will only know once he comes back from the specialist so we will have to wait and see. But we need to get to the root of the problem because it's pretty painful for him.

"Rob's comments have been taken out of context and his mental frame of mind is not the problem – it's the injury.

"Gavin hasn't played a lot of rugby and is the sort of player who needs games under his belt so he feels confident when he takes the field."

Henson aggravated his Achilles in an EDF Energy Anglo-Welsh Cup match for the Ospreys eight days ago which meant he could not train properly in the lead-up to playing the Springboks.

He eventually withdrew on Friday afternoon, 10 minutes after Howley had told a media briefing that he would definitely be fit. Gatland himself then said on Saturday, after Wales had lost 20-15 to South Africa, that the player might be fit in a week or two.

The interest in Henson, rated by Gatland as one of "our world-class players", is a regular occurrence in Welsh rugby. He courts attention like no other player except for Jonny Wilkinson and Danny Cipriani.

His career, to a lesser extent than Wilkinson's, has been stalled by injury. He suffered from an Achilles problem before the 2007 Rugby World Cup which eventually forced coach Gareth Jenkins to omit him from the squad.

Gatland, since his appointment last December, has made a point of encouraging Henson. He returned to the team for last season's Six Nations and played in all five games to record a major part in a second Grand Slam following the success, under Mike Ruddock, in 2005.

In between those Grand Slams, Henson has attracted plenty of attention on and off the field. Gatland remains a committed supporter and said last week: "We've been trying to encourage him, to give him the self-belief that he is a world-class player."

Gatland, meanwhile, has made 12 changes to the team for Friday's match against Canada at the Millennium Stadium. He had indicated that he would make full use of his squad and has also called up John Yapp, of Cardiff Blues, to prop because Duncan Jones has a foot injury.

Martin Roberts, the Llanelli Scarlets scrum-half, gains a Test debut in an effort to give him experience ahead of a likely appearance against Australia, on Nov 28, if the English-based Gareth Cooper and Dwayne Peel are not released.

Captain Ryan Jones, wing Leigh Halfpenny and centre Tom Shanklin are the three players to retain their starting places from Saturday's match against South Africa.