Wales lock Alun-Wyn Jones was set to undergo a scan Monday on a shoulder injury suffered in Saturday's defeat by Argentina, the Welsh Rugby Union announced in a statement.
Jones went off late in the first half of a morale-sapping 26-12 loss to the Pumas at Cardiff's Millennium Stadium and now his uncapped Ospreys colleague Lloyd Peers has been called up to train with the Wales squad as temporary cover ahead of Friday's match at home to Samoa.
However, centre Jamie Roberts could yet feature against the South Sea Islanders despite suffering what the WRU said was "mild concussion" against the Pumas.
Officials stressed Roberts was following agreed rugby protocols dealing with concussion injuries.
Meanwhile back-row forward Ryan Jones (shoulder) and centre Ashley Beck (hip) are on course to train fully this week.
However, Scarlets centre Jonathan Davies is still taking only a limited part in training due to a groin problem.
Flanker Dan Lydiate (ankle) and prop Adam Jones (knee) had already been sidelined from Wales's entire autumn series, which also includes Millennium Stadium matches against world champions New Zealand (November 24) and Australia (December 1).
In response to World Cup semi-finalists' Wales's injury problems, the announcement of the team to play Samoa has been put back 24 hours, from Tuesday to Wednesday.
The WRU said this would "allow coaches and medical staff further time to assess injuries and player recovery".
Six Nations Grand Slam champions Wales' defeat by Argentina was their heaviest home loss for three years and worst anywhere for 22 Tests.
Wales are currently sixth in the International Rugby Board world rankings, but further defeats in their remaining autumn Tests could see them drop out of the top eight.
That would leave Wales facing a tough task when the draw, based on the rankings, for the 2015 World Cup in England is made next month as it would mean they were in a group with two teams above them in the standings, with only two sides from each pool going through to the quarter-finals.