Sean O'Brien could return for Leinster, while Zebo and Conway are 50/50 for Munster.

With the Grand Slam celebrations now behind them, Leinster and Munster are both on the countdown towards their respective Champions Cup quarter finals, with contrasting fortunes on the injury front.

Leinster take on three-in-a-row chasing Saracens at the Aviva Stadium on Sunday, and have confirmed that Noel Reid, Dave Kearney and Jordan Larmour will all miss the game.

Reid and Larmour both departed Saturday's PRO 14 defeat to the Ospreys with injuries, while Larmour missed the game with a calf problem.

However in better news, both Sean O'Brien and Rhys Ruddock are in contention to make their returns at the Aviva Stadium. O'Brien suffered a shoulder knock just over two weeks ago, in what was his first game for almost three months. Senior coach Stuart Lancaster said he may be passed fit for the last eight game with Sarries.  

"Obviously it's more positive than we initially feared. 

"I think initially we we were worried it was going to be longer than this, but obviously he's done brilliant really, to put himself back in the mix."

Ruddock suffered a hamstring injury in December, and there were initial fears he would be out for the rest of the season, but Lancaster says he's very close to being fully fit.

"The one who's really done well on his rehab is Rhys Ruddock. He's passed all his markers, he's run his best fitness test, speed's good, so it's a real bonus to get him back in the equation," he added.

The outlook is much less positive for Munster.

With Tyler Bleyendaal, Keith Earls, Chris Farrell and Chris Cloete already confirmed absentees, Tommy O'Donnell is the latest to join them on the growing injury list.

The Tipperary flanker suffered a re-occurrence of the shoulder injury which has plagued him for much of the season, with head coach Johan van Graan confirming he'll miss this weekend's sold-out quarter final against Toulon at Thomond Park.

"He's very disappointed. Huge game coming up but he' a champion of a man, a fantastic Munster player, Munster man. He worked so hard, and the team always comes first. He had a big opportunity, but obviously that's gone now," van Graan said.

As well as Tommy O'Donnell's confirmed injury, van Graan will be sweating on the fitness of Rory Scannell, Simon Zebo and Andrew Conway.

Scannell is following the return to play protocols for a concussion sustained in Saturday's win against the Scarlets, while Simon Zebo missed that game with a hamstring injury. The versatile back did train today, but has been rated "touch and go" to recover in time.

Conway missed the entire Six Nations campaign with a knee injury, and is also in a race against time, according to Van Graan.