Ulster will be without both Rob Herring and Robert Baloucoune for Friday's BKT United Rugby Championship meeting with the Dragons at Kingspan Stadium.
Head coach Dan McFarland has made six changes from the side beaten 30-15 by Leinster in the Heineken Champions Cup round of 16, with Herring, Baloucoune and Rory Sutherland all listed as "unavailable" by the province.
Baloucoune's season has been blighted by hamstring issues, making just six appearances for the province, with Craig Gilroy coming in to replace him on the right wing this week, joining Mike Lowry and Jacob Stockdale in the back three.
It's an unchanged centre partnership of Stuart McCloskey and James Hume, while John Cooney - who last week agreed a new contract at Ulster - comes in for Nathan Doak at scrum-half, starting inside Billy Burns.
There are four changed to the pack, with two of them coming in the front row. O'Sullivan and Tom Stewart are drafted into the side, replacing Sutherland and Herring, with the pair joining Tom O'Toole in the front row.
Kieran Treadwell drops to the bench, with Sam Carter joining captain Alan O'Connor at lock, while the final change comes in the back row, where Marcus Rea comes in at openside to partner Duane Vermeulen and Dave McCann, with Nick Timoney held in reserve.
A win for Ulster would see them climb above the Stormers into second place, although the South African side would be able to move back into the top two on Saturday against Munster.
Ulster: Mike Lowry; Craig Gilroy, James Hume, Stuart McCloskey, Jacob Stockdale; Billy Burns, John Cooney; Eric O'Sullivan, Tom Stewart, Tom O’Toole; Alan O’Connor (capt), Sam Carter; David McCann, Marcus Rea, Duane Vermeulen.
Replacements: John Andrew, Andy Warwick, Jeffery Toomaga Allen, Kieran Treadwell, Nick Timoney, Nathan Doak, Stewart Moore, Ethan McIlroy.
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