<text>  It is the game which, ultimately, could define the success or otherwise of Martin ONeill and Roy Keanes expensive Republic of Ireland tenure. Installed amid much fanfare 18 months ago, 1million-per-year ONeill and his assistant Keane, with a 600,000 salary, were given a remit of qualification for Euro 2016, a task made easier by the expansion to a 24-team format. Defeat against Poland at the Aviva Stadium on Sunday evening, however, would all but end hope of automatic progression to the finals in France, leaving Ireland to do battle with Scotland for the play-off berth. The mood here is not optimistic. Martin ONeill, manager of the Republic of Ireland, needs to prove his worth with victory over Poland . ONeill and Roy Keane left were given big salaries and asked to reach the 2016 European Championships . An inquest, you feel, awaits ONeill and his regime should they fail to beat the group leaders. One newspaper described their manager as bookish and vaguely befuddled, and noted the carnage which follows Keane. There has been a definite effort to play down the chaos around Keane this week and the No 2 gave an untypically subdued and low-key performance in front of the press. ONeill ignored the opinion pieces which have called into question his impact since he arrived and kept all talk to football. He said: The importance of the occasion should not be missed. Defeat would be a big dent in our hopes of automatic qualification. It might not decide everything, but it is very significant. We have to try to win. If the Republic of Ireland fail to beat Poland, their hopes of automatic qualification will be all but over . ONeill and Keane take a training session at Gannon Park as the team prepare for Sundays big match . Ive said all along that the home games will shape our destiny. This is the first of that group. We have to make them count. We can change all of that negative talk with one result and one fantastic performance. We will not get very far with a pessimistic approach and Im not overly concerned with what people say before the game. We have given ourselves a chance of qualification but we will have to be right on top of our game to win this match. One criticism of ONeill is that he does not know his preferred XI or, indeed, formation. He said this week that players could win a starting place should they impress at their coastal training base in Malahide. Keane hands out instructions to the Republic of Ireland players during a training session . Sundays game takes place at the Aviva Stadium in Dublin; the Republic of Irelands home ground . One player not guaranteed to start is captain Robbie Keane. He was dropped for the morale-shattering 1-0 defeat in Scotland in November. The LA Galaxy striker, 34, said: Thats up to the manager if I play. Ill be ready whether thats from the bench or starting. Im the captain, I have to set an example. But I wouldnt be here if I didnt think I could make a difference. I still want to be the best. I have that hunger. Keane, sensing the air of negativity, added: Its up to us to make this a turning point. Victory would give this squad and country a huge confidence boost. Lose and it could prove an awfully long three months for ONeill before they host Scotland. Win, and that 1m salary would look like a shrewd investment. 