Leo Cullen warns that Leinster are facing an "ambitious and hungry" Ulster side in Saturday's Champions Cup sell-out last 16 clash at the Aviva Stadium (5.30pm).
Hugo Keenan returns for Leinster after completing his return to play protocols, but Garry Ringrose and Caelan Doris have been stood down for the weekend.
Along with the loss of club skipper Johnny Sexton after his groin op, the Blues will have to pull out all the stops in what is expected to be a tight affair, as it was when Leinster edged their 2019 quarter-final.
The Blues have won both URC fixtures between the sides this season but Cullen said: "They're a very efficient team, the way they play - and because they know us well, so they've a really good understanding of what we're trying to do.
"They've come out and said it plenty of times in recent years, their desire to win trophies, so they're clearly an ambitious, hungry bunch to do well.
"So we need to respect that. The game in the RDS was unusual, there was the red card and we'd a very slow start to that game.
"So we need to learn the lessons from that first 20 minutes so we're not in that situation where we have to chase the game to that extent.
Ringrose's place at outside centre goes to Jimmy O'Brien, who partners Robbie Henshaw, while Jack Conan gets the chance to back up his outstanding cameos off the bench in the Six Nations by taking Doris' place at no 8.
If Leinster progress to next week's quarter-final against Leicester or Edinburgh, Cullen expects to have Ringrose and Doris back.
"They're OK," he said. "Caelan was sick at the start of the week, so that's what ruled him out but he's come through OK.
"Garry should be OK to go next week...if there is a next week."
James Ryan skippers Leinster in the absence of Sexton, with Ross Byrne taking the no 10 role.
Ryan will be partnered by Ross Molony, who gets the nod ahead of Jason Jenkins in the second row. On the bench, hooker John McKee is in line to make his European debut.
While Leinster are still unbeaten this season after last week's rousing second half comeback against the second placed Stormers, Ulster come into the knock-out game on the back of three URC victories on the spin - and having put their early season woes behind them.
However Ulster are also missing their regular skipper with Iain Henderson sidelined with a forearm fracture suffered in Ireland's Six Nations win in Scotland.
Dan McFarland can call on a front row of Rory Sutherland, hooker Rob Herring and Tom O’Toole, who all featured during the Six Nations.
Kieran Treadwell, who was a late call-up for the Grand Slam clincher against England, will be partnered in the second row by stand-in captain Alan O'Connor.
Nathan Doak retains the scrum-half jersey while Stuart McCloskey, who started the first three Six Nations games for Ireland, will relish going up against Henshaw.
“We have the ability to win games against Leinster, but we are also aware that if we’re not playing to the peak of our ability, it’s going to be tough going," said Ulster head coach Dan McFarland.
"We are very motivated about the opportunity that lies ahead of us on Saturday.”
LEINSTER: Keenan, Larmour, O'Brien, Henshaw, Lowe, H Byrne, Gibson-Park; Porter, Sheehan, Furlong, Molony, Ryan, Baird, van der Flier, Conan.
Replacements: McKee, Healy, Al'alatoa, Jenkins, Penny, McGrath, H Byrne, Frawley.
ULSTER: Lowry, Baloucoune, Hume, McCloskey, Stockdale, Burns, Doak; Sutherland, Herring, O’Toole, O’Connor, Treadwell, McCann, Timoney, Vermeulen.
Replacements: Stewart, O’Sullivan, Toomaga-Allen, Sheridan, Rea, Cooney, Moore, Moxham.
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