Leinster's cross to bear is that they are the perennial favourites against any team that arrives in Donnybrook.

This is a reflection of the perceived strength of the squad and the reputation of the Donnybrook ground but if the knocks picked up at the province's training session yesterday to Brian O'Driscoll, Shane Horgan and Christian Warner are serious, that notion of invincibility will surely come under threat.

The outhalf and two centres will need medical clearance at lunchtime today before they line out. O'Driscoll pulled up with a hand problem, while Horgan and Warner have quadriceps and hamstring difficulties respectively.

There may yet be a start for Argentinian outhalf Felipe Contepomi, who is among the replacements.

It would be a blow to coach Mark Ella if any of the three was forced to pull out today but counterpart Alan Solomons will nonetheless be leading his Ulster side into what he considers is another battle in which they will have to punch above their weight to take anything back to Belfast.

What would be quite a task at any time has been exacerbated by the fact the Ulster squad have not been able to practise on any outdoor pitch because of the freezing weather.

"We haven't been on a practice pitch for two weeks. We've had to work in the gym because the pitches have been frozen," Solomons said yesterday. "That has been disappointing as we are pretty much up against a team that is one of the strongest in the competition."

Solomons has been around for long enough, however, to understand that the formbook frequently goes out the window when Irish provinces face each other, and that teams which might look unbalanced on paper often seem to level out when they take the pitch.

There were also enough sour grapes in the Ulster province about the make-up of the Irish World Cup team (largely Leinster and Munster players) that one can also assume a number of players will be travelling to Dublin with the belief that this is as much an Irish trial as a mid-point Celtic League match.

With Ireland looking towards their first Six Nations match on February 14th, a number of players will want to impress more people than Solomons.

Ulster, the frozen ground aside, do have momentum with them and have come out of two hard back-to-back matches with their reputation enhanced. Their wins over Stade Francais and Edinburgh will have done a lot for morale.

Resilient defence against Edinburgh paid big dividends and this allied to a streetwise approach to the wet conditions earned them two tries and three penalties in the first 40 minutes,

Ulster have also shown themselves to be a canny unit. Shane Stewart and Paul Steinmetz will again try to hold the centre tight, where O'Driscoll and Horgan are expected to pose the most significant Leinster threat, with two internationals Tyrone Howe and James Topping on the flanks.

David Humphreys will call the shots while the front row of Robbie Kempson, Matt Sexton and Simon Best have been increasingly effective.

Solomons believes Kempson is the best loosehead prop in world rugby. "Obviously a player like Robbie would play for South Africa if he were available. We've punched considerably above our weight and this is another week in which we will have to do it," said the coach.

Tactical kicking, a big front-row effort and sound defence will hope to advance the Ulster cause, while Ella's side are likely to be less strictly drilled and more inclined to run with ball in hand given the opportunity, although, as ever, footholds will first have to be gained up front.

Brendan Burke on the Leinster wing ought to bring his usual dynamism to the game, having lost pitch time recently to injury, while Aidan McCullen joins Victor Costello and Keith Gleeson in a strong back row that faces a tigerish if inexperienced duo in Neil Best and Roger Wilson alongside war-horse Andy Ward.

Precautionary measures have kept the back-rower Eric Miller (shoulder) and full-back Girvan Dempsey (hamstring) out of the side while Gary Longwell is again omitted from the Ulster squad.

Gordon D'Arcy at 15 has regularly shown his attacking ability but with both Humphreys and his opposing full back, Paddy Wallace, kicking at him, his awareness and tactical acumen will also be questioned in what is a big game for both young full backs.

Attention will also focus on the midfield, not least on the partnership of Warner and Brian O'Meara. Contepomi will probably show at some stage but with Ella holding to team continuity as Leinster's Heineken European Cup match against Sale approaches, the selection seems prudent.

The stand sold out already at Donnybrook, Leinster expect a sizeable crowd and ask for supporters not to turn up at the last minute to see if Leinster can threaten Ulster's three-point cushion at the top of the table and dent their hopes of the Celtic League and Cup double.

Last time they met, in October, Ulster won on a try count-back after extra-time. But that Leinster team isn't this one and Ulster know that too.

LEINSTER: G D'Arcy; J McWeeney, B O'Driscoll, S Horgan, B Burke; C Warner, B O'Meara; R Corrigan, S Byrne, P Coyle, M O'Kelly, B Gissing, A McCullen, K Gleeson, V Costello. Replacements: J Moran, G Hickie, D Dillon, S Jennings, B O'Riordan, F Contepomi, D Quinlan.

ULSTER: P Wallace; J Topping, S Stewart, P Steinmetz, T Howe; D Humphreys, N Doak; R Kempson, M Sexton, S Best, M Mustchin, R Frost, A Ward, N Best, R Wilson. Replacements: R Moore, P Shields, M McCullough, W Brosnihan, K Campbell, A Larkin, B Cunningham.

Referee: N Owens (Wales).