Assistant coach Rob Howley says Wales remain hopeful of having Rhys Priestland, Jamie Roberts and Dan Lydiate fit for Sunday's RBS 6 Nations opener against Ireland in Dublin.
Scarlets fly-half Priestland and Cardiff Blues centre Roberts are struggling with knee injuries, while Newport Gwent Dragons flanker Lydiate has an ankle problem.
All three played a part in last week's pre-tournament training camp in Gdansk (Spala), Poland, and Wales have delayed naming their side for the Aviva Stadium clash until Friday to give them the best chance of being involved.
But Howley says it will be their response to training over the next two days that will determine their availability.
He said: "Last week went well, obviously with Dan Lydiate and Rhys Priestland we are still waiting. In terms of their participation, it was very limited last week.
"Dan and Rhys probably did about two or three sessions but they were just limited to skills, the next 48 hours is pretty critical and we are waiting to see how they are.
"They have come in this morning and they are a little bit sore after the weekend's endeavours but we are obviously hopeful.
"Jamie participated a little bit more than Dan and Rhys but we are still uncertain. Jamie has not played for a long time, I think it's around five or six weeks, so we are, once again, waiting to see how the next 48 hours goes."
Should Priestland, who played a starring role at the World Cup, be ruled out, James Hook will likely take the number 10 shirt with Stephen Jones or Gavin Henson able to provide bench cover.
Henson would also be an option at centre if Roberts loses his fitness battle, with young Osprey Ashley Beck and Scott Williams being among Wales' other midfield options.
Ryan Jones and Andy Powell are potential replacements for Lydiate in the back row.
Wales are already without the likes of prop Gethin Jenkins and the first-choice lock pairing of Alun Wyn Jones and Luke Charteris.