Joey O'Brien was expected to leave the Republic of Ireland squad on Sunday after undergoing a scan on a hamstring injury.
The West Ham defender was sent for tests on Saturday after reporting a problem during the warm-up ahead of the previous night's 3-0 friendly victory over Latvia.
Midfielder Andy Reid returned to his club, Nottingham Forest, on Saturday with a similar injury.
However, central defender Seán St Ledger, who was also a doubt, was expected to remain with the party which was scheduled to fly to Poland on Sunday afternoon.
Reid suffered his injury during training in Malahide on Saturday morning.
The Dubliner, who came on for around 20 minutes on Friday evening, has only recently returned to the squad after five years in exile during Giovanni Trapattoni’s tenure, and was expected to play some role in Poznan.
The players will fly out to Poland on a high, having turned in one of their most convincing performances for some time against a Latvia side which did little to upset the script.
O'Neill knows few of their future opponents will prove quite as submissive as Marian Pahars's men on a night when goals from Robbie Keane – the 62nd of his senior international career – Aiden McGeady and substitute Shane Long secured a comfortable win.
However, the manner in which Ireland played, with wingers Aiden McGeady and James McClean terrorising their markers and James McCarthy and Wes Hoolahan pulling the strings behind Keane, drew a line under the safety-first approach of Giovanni Trapattoni.
Ireland may not always be able to take the same aggressive stance against more dangerous opponents, but the knowledge that the ability to do so remains in the armoury is a comfort.
“We can’t get carried away with ourselves,” O’Neill said on Saturday. “Lots of things could happen. When the big games come in, it’s a matter of having your best players available, and that might not always be the case. I felt the performance was excellent. I mentioned last night, there will be sterner tests than Latvia, but it was good.
“It was good to play, it was good for players to get a bit of confidence about themselves. I think they felt that with the crowd behind them as well, it was positive for a first game. You mentioned how important it was to win the game – of course, the winning of the match is vitally important.”
Poland, who pushed England all the way before losing 2-0 at Wembley in their final World Cup qualifier last month, will provide very different opposition in a city where Ireland lost to Croatia and Italy during their ill-fated Euro 2012 finals campaign.
O'Neill will make changes – David Forde will definitely start in goal after Keiren Westwood got the nod against the Latvians.
From a personal point of view, O’Neill insisted he remains as hungry for success now as he was as a teenager launching his career in professional football.
“That hunger is there from – it was there from starting out as a player, as an 18-year-old. I haven’t felt any sort of changes. Of course there are ups and downs and everybody has experienced those things, but overall it feels the same.”
Asked if he is still driven on by the same things which brought him into football in the first place, he added: “Very much so, and this is it: it’s just raw enthusiasm for the game. Those things never change, really. The minute that they do change, that’s when you want to re-assess things.”
