Wingers Shane Williams and Mark Jones must prove their fitness to Wales head coach Gareth Jenkins by Wednesday if they are to be considered for Sunday's RBS 6 Nations clash with Ireland.
Jones rates his chances of recovering from ankle ligament damage as only 50-50 while Williams struggled with his movement in training on Tuesday and was not overly optimistic of shaking off a nagging hip injury.
Jonathan Thomas is available after recovering from a shoulder injury, but the Newport Gwent Dragons flanker expects only a limited involvement at best this weekend because of his short preparation time.
Thomas only joined the squad for training on Tuesday and Wales have other in-form options on the blindside flank including Alix Popham and Colin Charvis.
Jenkins names his team on Thursday afternoon and also has the added complication of Gareth Thomas' European Rugby Cup disciplinary hearing to deal with.
Williams said: "I want to be playing on Sunday and I have been training my nuts off - I literally mean that! - to get back in time.
"Now it is make-or-break time. It is only fair on Wales if I make my mind up this (Wednesday) afternoon.
"It has been a hard couple of weeks. The injury is in an area where I only need to cough to be reminded of it. It is an injury that no-one has - and I have had it twice. It is unbelievable.
"I struggled doing a few things in training yesterday (Tuesday) that I would do easily on another day and you need to be 100% to play Ireland.
"It will be disappointing if I miss out because I feel this year has gone well for me so far.
"I said to myself in pre-season that this would be an important year for the Ospreys and Wales, with all the tournaments and tours.
"I feel I have played well. This is just bad timing."
Jones' ankle injury affects his sprinting and he still hopes to be available for selection - but the next 24 hours are crucial.
He said: "I am still positive. Everything I have been asked to do has gone well.
"I want to play more than anything in the world but when you cross that whitewash you are fit in everybody's eyes and you are judged on that.
"I won't know until we see how it reacts to training and I won't put the team in jeopardy if it is not right."
As head coach Stuart Lancaster polishes the axe he will soon wield over his World Cup training squad, Exeter Chiefs coach Rob Baxter has backed Jack Nowell, Henry Slade and Luke Cowan-Dickie to be given a stay of execution.
Italy Under-20s held off a late Samoa blitz to retain their place in the World Rugby U20 Championship on Saturday and head coach Alessandro Troncon believes the experience will have served as a valuable lesson for his young troops.