Sammon is perhaps a controversial choice to line up alongside West Brom's Shane Long in attack with Jon Walters once again asked to patrol the right side of midfield and Simon Cox, the recalled Kevin Doyle and highly-rated Norwich playmaker Wes Hoolahan held in reserve.

But Trapattoni was making no apologies for selecting the npower Championship striker.

Asked why he had picked Sammon, who was used as a substitute in Sweden on Friday night, the Italian replied: "Because I think his quality can give Shane support.

"Physically he is strong enough, he's quick and he is good in the air and he showed us good quality in the last game. He is not only tall, he is fast as well.

"Long is fast as well and we need two fast players. It's important to defend the ball and give this support to allow the team to come up [the pitch].

"We don't know how Austria will play - will they come and press us or will they stay and wait for us?

"Will they wait for us and hit us on the counter-attack, or will they come and put pressure on us? Will they give us the space or will we find to find the space?

"That's why we need these two fast players."

The Boys in Green did not muster a single attempt on target as they secured their 0-0 draw in Stockholm, and without Keane, they will be deprived of their 54-goal record scorer.

Neither Long nor Sammon have been particularly prolific for their respective clubs this season, although Trapattoni was quick to defend his frontmen.

He said: "I said to Kevin Doyle this morning: 'I know how difficult it is for you to play at your club'. It's difficult for a striker to play alone and without support.

"How is it possible to play against three or four defenders and score a goal? Only Maradona and [Lionel] Messi, big players like that, can do that.

"It's important for us to give support to our strikers. But also, Sweden had no opportunities to score against us - apart from one, maybe."

Trapattoni revealed he took the decision not to start with Hoolahan because he sees him as an out-and-out number 10 whose best work is done in a very specific area of the pitch, and he sees Sammon's pace and physicality as weapons better suited to the task of taming the Austrians.

There will be invention in the team in the shape of Wigan's James McCarthy, although his 74-year-old manager has threatened to take drastic action in a bid to get the best out of him.

Trapattoni said with a smile: "I told him, 'I will punch you if you don't stop being shy'.

"He's a very good player. He is only 21, but he can improve and take more confidence. Every training session, I see he has the qualities to dominate opponents.

"He has those qualities already, but he has to improve in confidence."

Apart from Keane's absence and Sammon's introduction, Trapattoni intends to make only one further change with Glenn Whelan returning from injury in place of Paul Green, although he has a concern over left-back Marc Wilson, who is nursing a groin problem.

However, Ireland will head into the game confident they can take a major step towards claiming the runners-up spot by collecting three points.

Trapattoni said: "We have shown we are a good team, compact with good personality. The players played with conviction and good attitude [in Sweden] and are growing in belief that we can qualify.

"We must try win this game, but we must also play with intelligence because there are many games to come before qualification is finished.

"We have to be in contention until the very last game. It will be important to stay up with Sweden because Germany are too far ahead.

"But I have a lot of trust in this group and I am convinced we can improve even more."