The 25-year-old underwent a scan today, on the injury which forced him off after 38 minutes of Saturday's provincial derby, and it revealed a broken bone in one of his fingers.
It is expected that the Irish international - who broke Diego Dominguez's Heineken Cup record of 645 points in last month's 36-8 win over Castes - will be out for at least three weeks, meaning Paul Burke is likely to deputise next Saturday against the Neath-Swansea Ospreys at Thomond Park, and on January 15, against his former employers NEC Harlequins at Twickenham.
The unfortunate O'Gara has enjoyed a stunning start to the 2004/05 season, scoring all of Ireland's points in their autumn wins over South Africa (17-12) and Argentina (21-19).
The Corkman has also bagged 86 points for Munster in nine games - with 41 of those coming in the Heineken Cup action.
O'Gara kicked two penalties before departing the scene at Musgrave Park. Second half tries from Marcus Horan and Frankie Sheahan were to help Alan Gaffney's to a deserved victory, as they held off Leinster's late charge.
Gaffney's men moved a single point behind leaders, the Ospreys, once more, as they went 19-3 in front through their maul try double on 52 and 60 minutes.
Declan Kidney's visitors managed to breach the home line late as flanker Eric Miller was on the end of a left-to-right move, involving prominent play from Gordon D'Arcy, Brian O'Driscoll and Ben Gissing - but not even their 10-point haul in the final 14 minutes could prevent Munster from winning in cold conditions.
O'Gara's replacement Burke kicked a penalty in first half injury time but failed with the two conversions, while Leinster's number 10 David Holwell - who turns 30 on Friday - managed to flight a brilliant convert of Miller's effort to add to his two earlier penalties.
Munster 19 Leinster 13, Musgrave ParkScorers: Munster: Tries: Marcus Horan, Frankie Sheahan; Pens: Ronan O'Gara 2, Paul BurkeLeinster: Try: Eric Miller; Con: David Holwell; Pens: Holwell 2
(15) Christian Cullen(14) Shaun Payne(13) Mike Mullins(12) Rob Henderson(11) Anthony Horgan(10) Ronan O'Gara(9) Peter Stringer(1) Marcus Horan(2) Frankie Sheahan(3) Gordon McIlwham(4) Donncha O'Callaghan
Replacements used: Paul Burke for O'Gara (38 mins), Jim Williams for Foley (59), Mossy Lawlor for Henderson (70). Not used: Jerry Flannery, Mike Storey, Trevor Hogan, Mike Prendergast.
(15) Girvan Dempsey(14) Shane Horgan(13) Brian O'Driscoll(12) Gordon D'Arcy(11) Denis Hickie(10) David Holwell(9) Guy Easterby(1) Reggie Corrigan (Capt)(2) Shane Byrne(3) Emmett Byrne(4) Leo Cullen(5) Ben Gissing(6) Eric Miller(7) Shane Jennings(8) Victor Costello
Replacements used: Ricky Nebbett for E Byrne (63 mins), Ciaran Potts for Gissing (76). Not used: David Blaney, Aidan McCullen, Brian O'Meara, Felipe Contepomi, Kieran Lewis.
Half time: Munster 9 Leinster 3; Attendance: 8,000Referee: Alan Lewis (IRFU)