Dwayne Peel is the latest Wales injury scare ahead of the Grand Slam winners' bid to beat South Africa in June.
The Scarlets' scrum-half has a shoulder injury that rules him out of Warren Gatland's 24-man training squad.
With Gareth Cooper part of Gloucester's Guinness Premiership play-off push and Mike Phillips out, London Irish's Warren Fury, 22, comes in.
Scarlets full-back Morgan Stoddart and Dragons scrum-half Andy Williams are also fresh faces since the Six Nations.
Gatland said: "Andy Williams and Morgan Stoddart both have a chance to show the coaches what they have to offer and to book themselves a seat on the plane to South Africa.
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"Andy and Warren in particular are in with a good shout with two injuries in their position, to Mike Phillips and Dwayne Peel, being a worry for us."
Gatland remains hopeful Peel and ankle-injury victim Gavin Henson will be fit to take on the World Champions.
Henson's regional team-mates Lee Byrne and Sonny Parker will also undergo fitness tests on knee injuries to determine whether or not they should be at the training camp.
Wales will train in Wexford, Ireland for a week from next Monday. If Newport-Gwent Dragons are involved in a Heineken Cup qualification play-off, Williams and Rhys Thomas are likely to be released to their region.
"We have been given the opportunity to go on a pre-tour training camp thanks largely to the support of the four regions in Wales"
Gareth Delve joins Cooper as an absentee due to Gloucester commitments.
Gatland said: "We have been given the opportunity to go on a pre-tour training camp thanks largely to the support of the coaches and management at each of the four regions in Wales.
"This is not something that we will be able to do every year, because I would like to see our regions in contention for end of season honours.
"But, with no European competition left at the end of a tough season and with Leinster runaway leaders of the Magners League, we have been able to negotiate a position which will hopefully be of benefit to everyone.
"The regions have allowed us to take the players away for an intensive period of training in advance of our tour to South Africa and I would like to personally express my gratitude for their co-operation."
Gatland will take his side to a training base in Wexford that specialises in Cryotherapy, which aids the body's recovery from exercise and allows more training.
"This is our core group now, but there may also be one or two other names we add to the tour party injuries permitting and with a couple of players down in England not considered at the moment," added Gatland.
Wales will announce their tour squad on May 14.
Wales training squad:
Backs: Morgan Stoddart, Lee Byrne, Jamie Roberts, Shane Williams, Tom James, Sonny Parker, Tom Shanklin, Stephen Jones, James Hook, Andy Williams, Warren Fury.
Forwards: Duncan Jones, Gethin Jenkins, Rhys Thomas, Adam Jones, Matthew Rees, Huw Bennett, Ian Gough, Alun Wyn Jones, Ian Evans, Jonathan Thomas, Martyn Williams, Alix Popham, Ryan Jones.
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