Ronan came on as a replacement for Muldoon in the 73rd minute of the game against the baby Boks and his selection means a re-shuffle in the back-row, with captain Stephen Keogh moving to blindside flanker and Ciaran Potts anchoring the Irish scrum.
It's a must win game for both sides for different reasons. The Irish can progress to the latter stages if they win their remaining games and gain a bonus point and the Scots are in a similar position although with a different objective in that two victories (plus a bonus) will see them battling to finish playing off for fifth to eighth place in the tournament.
For their part Scotland make five changes in the starting line-up from the one beaten 37-19 by Wales on Friday. Three of those have been forced, and arguably the biggest loss will be Chris Cusiter who suffered knee-ligament injury injury in that game and he will take no further part in the tournament. Mark McMillan, the Stirling County scrum half replaces Cusiter in what will be his first international outing at this level.
Medical exams rule out prop, Geoff Cross and his place goes to Dundee tight-head, Alasdair Dickinson who played against the Irish in the championship game back in February.
Ireland. 15. Peter O'Brien - UCC14. Keith Matthews - UL Bohemians13. Barry Murphy - UL Bohemians12. Glen Telford - Instonians11. John Hearty - Blackrock College10. Michael Rainey - Glasgow Hawks9. Fiach O'Loughlin - Shannon8. Ciaran Potts - St. Mary's7. Niall Ronan - Lansdowne6. Stephen Keogh - UCC capt 5. Neil McComb - Dundee Highschool4. David Gannon - UCD
Gareth Morton (The Borders); Nikki Walker (The Borders), Graeme Morrison (Glasgow Hawks), Philip Godman (Newcastle Falcons), Andrew Turnbull (Watsonians); Alistair Warnock (Boroughmuir and Scottish Institute of Sport), Mark McMillan (Stirling County and Scottish Institute of Sport); John Malakoty (Glasgow Hawks), James Henry (Leicester Tigers), Alasdair Dickinson (Dundee HSFP and Scottish Institute of Sport), Alasdair Stroksoch (Boroughmuir and Scottish Institute of Sport), Mark Rennie (Newcastle Falcons), Steve Swindall (Glasgow Hawks), Allister Hogg (Edinburgh Rugby and Scottish Institute of Sport) captain, Kelly Brown (Melrose and Scottish Institute of Sport). Replacements. Fergus Thomson (West of Scotland and Scottish Institute of Sport), Gavin Mories (Glasgow Hawks), Stuart Male (Glasgow Hawks), Tom MacCormick (Harlequins), Brendan McKerchar (Durham University), Tom Philip (Edinburgh Rugby and Scottish Institute of Sport), Colin Shaw (Glasgow Hawks).