The 26-year-old Preston defender has been unable to train since damaging a knee in a training ground collision with Ciaran Clark on Tuesday morning, and time is running out fast for him to prove he can line up alongside Richard Dunne at the weekend.

St Ledger will be assessed tomorrow, when Trapattoni will have to make a call in the face of a growing injury crisis.

Goalkeeping coach Alan Kelly said last night: "We are giving him as much time as possible. Twenty-four hours can make a big difference and we will see what he is like tomorrow.

"The problem is around the knee area. It was boot to boot - he kicked Ciaran Clark's leg. It was an impact injury, so he will be assessed tomorrow."

If St Ledger does not make it, Clark could be one of the candidates to replace him having initially being penned in as a possible contender for the left-back spot along with Kevin Kilbane.

Kelly was giving little away on the manager's thinking on that front, insisting instead that the next 24 hours could yet bring good news.

He said: "Obviously he [Clark] has done very well for Aston Villa in a defensive role, but we will have to wait and see.

"You are discounting Sean St Ledger too soon. As I say, 24 hours is a long time."

In the circumstances, Dunne's continued presence on the training pitch represents a major boost for Trapattoni with the Villa defender seemingly having recovered from his shoulder problem.

But with keeper Shay Given and full-back John O'Shea both sidelined by injury, St Ledger's loss would leave Trapattoni's first-choice defence in tatters.

The squad was reduced further last night when Everton midfielder Seamus Coleman was withdrawn after his ankle injury was assessed, following Newcastle striker Leon Best on his way back to England.

But experienced winger Damien Duff had earlier trained for the first time since arriving with an inflamed Achilles tendon.

Kelly said: "You saw me dragging Duffer off the training pitch, which is always a good thing to see.

"He's looking as fit as ever. He's done a full session today, so that's a massive plus for us."

Whatever team Trapattoni is able to field on Saturday evening, he is likely to stick with the 4-4-2 formation he has steadfastly employed since his arrival in Ireland, a topic which has sparked a concerted debate since the 3-2 defeat by Group B leaders Russia in October.

However, he remains unmoved, and Kelly was perfectly on-message when questioned on the subject.

He said: "When you have seen the results we have got, especially against the big teams and how we have played, we have just got to do what we did against those teams.

"Whatever formation that may be, whatever brings the results is the road we will go down."