MARTIN O'NEILL believes that most of the pressure weighs on his Republic of Ireland side as he makes preparations for Saturday's make-or-break qualifier against Scotland in Dublin.

O'Neill was in good form in a sun-drenched Dublin yesterday, reporting that John O'Shea was his only concern having sustained a calf injury in the dull 0-0 friendly with England on Sunday and a small concern at that.

If Sunday's friendly against England was less instructive, the Irish manager revealed he had fielded a three-man defence in last week's closed-doors friendly against Northern Ireland with Seamus Coleman and Robbie Brady stationed as wing backs in anticipation of Saturday's game. O'Neill said he may deploy the tactic again should Scotland take the lead in the Aviva Stadium.

"I don't see why we shouldn't consider that option and we have done little bits of practice here and there with it," admitted O'Neill with a rueful smile. The Irish are notorious for playing 4-4-2.

"Essentially, in the game against Northern Ireland, we did have that, Seamus pulling wide on one side, Robbie pulling wide on the other" admitted O'Neill, "We have to try and win the game."

"So whatever formation we use, I use that advisedly because eventually players win games" proclaimed the Irish manager, who has stuck rigidly with four defenders since taking charge of the Republic in November 2013.

"Essentially we played three players in the midfield," O'Neill said of the England game. "Starting with Aiden [McGeady] on the left side and players can move around, Aiden was getting a bit of joy down the left, so he decided to stay there."

The Irish have only kept one clean sheet in the Euro 2016 campaign. It came in October's 7-0 home thrashing of lowly Gibraltar. Clearly, defence is a significant concern for O'Neill's side, who have conceded at a rate of almost a goal a game since the Derry man took charge.

In the five Euro 2016 qualifiers to date Ireland have fell behind three times and needed last-minute goals to rescue points against Germany and Poland, while McGeady snatched a last-second winner in Georgia.

In an effort to shore up and increasingly leaky defence, O'Neill recalled the 39-year-old Shay Given for the Poland game but his rationale for doing so left many scratching their heads after claiming that the Aston Villa goalkeeper "had a wee bit more experience" than David Forde. Forde is 35.

The other end of the field has not brought much cause for celebration either, that thrashing of Gibraltar aside, Ireland have found the net just four times, including a double for McGeady against Georgia.

There does not appear to be a ready-made solution, either. Of the 106 international goals scored by the 27-man panel, Robbie Keane has scored 65 and Shane Long 11, the remaining 22 outfield players have shared 41 goals. O'Neill is suitably aware of the deficiencies.

"I think it was would be nice to get in front in a game rather than chasing games" admitted O'Neill, "I think we're capable of keeping sides out, there's always a possibility of conceding a goal like in Scotland."

"The problem is really getting enough goals, I was asked yesterday on what we could improve on," explained O'Neill. "Obviously, getting chances in a game and taking them.

"It is nice to have natural goalscorers in the team and if we don't possess them, well Robbie is coming back. But, if he didn't, then we have to try and find other ways to try and win the game."

For all other ills, there is the three-man defence. Paul McShane, who ended the season with Hull City but who is likely to move on over the summer, used to the system at club level. He also knows a thing or two about Andy Robertson, his soon-to-be former clubmate and the man who tormented the Republic's defence in Scotland's 1-0 victory at Celtic Park back in November.

Asked how McShane and Ireland would deal with his threat from the left, McShane said: "I'll bury him!"