Venue: Ravenhill Date: Tuesday, 13 April Kick-off: 1930 BST
Coverage: Live on BBC Radio Ulster medium wave and S4C, score updates on BBC Sport website
Paddy Wallace moves from centre to full-back for Ulster
Paddy Wallace switches to full-back for Ulster's Magners League clash against the Ospreys on Tuesday evening.
Ian Whitten replaces Timoci Nagusa while Bryan Young, Dan Tuohy and Robbie Diack are drafted into the pack.
The Ospreys make three changes to the side that lost 29-28 to Biarritz in the Heineken Cup quarter-final on Saturday.
Sonny Parker, Ian Gough and Ryan Bevington start with Andrew Bishop, Alun Wyn Jones and Paul James dropping to the bench.
With Tom Court named on the Ulster bench after recovering from a neck injury, Young replaces Declan Fitzpatrick at prop while the other pack changes see Tuohy and Diack taking over from Ryan Caldwell and David Pollock.
Simon Danielli made a late switch to full-back for the last outing against the Blues after Jamie Smith was ruled out by injury but with Wallace wearing the number 15 jersey, Danielli returns to his normal wing berth.
Ulster's back-to-back defeats by Cardiff left them in eighth place in the table and coach Brian McLaughlin is demanding an improved display against the Ospreys.
"Losing at Ravenhill is not something that is taken lightly," said McLaughlin.
"Playing in front of your home crowd means so much to each player and each coach, so we all know what is required of us come Tuesday.
"Last week against Cardiff we simply weren't good enough," added McLaughlin.
"We made a strong start, but went on to give away too many soft points. It was very disappointing because we know we can win these games.
"It will be a very tough game for us, but we have to make sure we're in their face and don't let them play. We will not gift Ospreys such easy scores.
"We have to make sure we are up for the game, we have to compete and we have to make sure we beat them at Ravenhill.
"We have to go to town with them up front and show that we are more than capable of dealing with them.
"We all know not to under estimate them. Ospreys are a dangerous side, who can and do compete at the highest level, so we need to ensure we give them nothing to play with."
It's a quick turnaround from Saturday... but we can't feel sorry for ourselves
Ospreys coach Sean Holley
Ulster have won just one of their last eight league matches and have not beaten a Welsh region in 2010.
Ospreys have won on their last two trips to Ravenhill, but lost the reverse fixture in Swansea 20-16 in September and Ulster will be seeking a first league double over them.
The Ospreys, coming off the back of their agonising loss to Biarritz, will be without the injured Ross Davies, Duncan Jones, Tom Isaacs, Lyndon Bateman, Tom Smith, Barry Davies and Richard Hibbard.
"It's a test of character for us now, the Biarritz defeat was a massive disappointment," Ospreys coach Sean Holley told BBC Sport Wales.
"It won't be easy, but we have to get back on the horse for Ravenhill on Tuesday and Dublin on Friday.
"Those two games are going to determine to a large extent how well we do in the Magners League.
"It's a quick turnaround from Saturday, which will be a test of our fitness and conditioning, as well as our character and spirit, but we can't feel sorry for ourselves."
The Ospreys, who need a point to guarantee Heineken Cup qualification for next season, are one point behind Glasgow, who occupy the final play-off place, two behind Edinburgh and Munster and nine behind leaders Leinster.
The first-placed team will be home to the fourth and the second-placed team home to the third in the play-off semi-finals.
The Ulster match is the game in hand that the Ospreys have on all the sides above them except Leinster.
But that could yet complicate their run-in, the Ospreys' late call-off of the original Ravenhill date the subject of a Magners League investigation next Monday that could, potentially, see the Liberty Stadium side docked points.
Ulster: Paddy Wallace, Andrew Trimble, Darren Cave, Ian Whitten, Simon Danielli, Niall O'Connor, Isaac Boss, Bryan Young, Rory Best, BJ Botha, Ed O'Donoghue, Dan Tuohy, Stephen Ferris, Chris Henry (capt), Robbie Diack. Replacements: Andi Kyriacou, Tom Court, Ryan Caldwell, David Pollock, Paul Marshall, Ian Humphreys, Nevin Spence
Ospreys: Lee Byrne; Tommy Bowe, Sonny Parker, James Hook, Shane Williams; Dan Biggar, Mike Phillips; Ryan Bevington, Huw Bennett, Adam Jones, Ian Gough, Jonathan Thomas, Jerry Collins, Marty Holah, Ryan Jones (capt).
Replacements: Ed Shervington, Paul James, Alun Wyn Jones, Filo Tiatia, Jamie Nutbrown, Andrew Bishop, Nikki Walker.
Referee: Neil Paterson (SRU)