Scotland's injury problems increased on Tuesday with the withdrawal of hookers Rob Russell and Steve Brotherstone ahead of the Six Nations Championship clash against Wales at Murrayfield on Saturday.

Russell, of English Premiership club Saracens, had originally been promoted as back-up to Gordon Bulloch, the first choice hooker after Brotherstone's 11th-hour decision to pull out of the squad to play against France in Paris a fortnight ago.

But Brotherstone had responded well enough to treatment to be named on Monday in the Scotland A team to face Wales A in Edinburgh on Friday.

But the revelation by Scotland forwards coach Hugh Campbell that both Russell and Brotherstone had suffered recurrences of their shoulder and knee injuries respectively, means that the senior side are without a back-up hooker and the A team need to find two players in that position too.

Bulloch is now assured of his position in the starting line-up that coach Ian McGeechan will unveil on Thursday.

Forwards coach Campbell said: "Russell has an on-going shoulder injury that has troubled him for some time.

"It was evident this week that while he could perform some skills, he was unable to throw consistently well.

"Brotherstone had hoped to play for Northampton last Saturday but decided he had not recovered sufficiently to play at the weekend."

But Campbell dismissed suggestions that Scotland's plans had been severely disrupted as a result of the growing catalogue of injuries.

"We are very fortunate to have a number of players in that position who could perform at international level - it is one area where we have strength in depth."

Steve Scott, the Edinburgh Reivers' hooker, is now expected to be drafted into the senior squad as cover for Bulloch.

"Scott was with us in New Zealand and was capped as a replacement at Eden Park. He is familiar with the things we do. I believe he will fit in very well. I'm also happy at the way the four hookers are performing at the moment," said Campbell.

He insisted Scotland had to get the scrum right against Wales.

"I was unhappy at our inconsistency in Paris (Scotland lost 16-6)," he said. "We scrummaged well at times against France, but also lost our focus at times."

Wales, he said, would offer a considerable threat. "Wales pose a significant threat in the scrum. At times, they drove England off the ball in Cardiff. They will test us severely in that area."

Meanwhile, Campbell confirmed that giant Edinburgh Reivers lock Richard Metcalfe had come through a rigorous training session on Monday and had been declared fit to play.

Metcalfe dislocated a finger in the 16-6 defeat to France and was replaced by Newcastle lock Stuart Grimes. Metcalfe will once again partner Scott Murray in the second-row, with Grimes likely to be used mid-way through the second-half as an impact player.