Doak injured his ankle in the last 16 win over Ospreys but recovered to start in Belfast alongside the returning Jack Murphy.
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However, hooker Rob Herring is not in the matchday squad after suffering a calf injury.
Tom Stewart will start in place of Herring, and will be joined in the front row by Australian prop Angus Bell and Tom O’Toole.
Cormac Izuchukwu will make his 50th Ulster appearance in the second row with captain Iain Henderson, while David McCann, Nick Timoney and Juarno Augustus make up an unchanged back row.
Stuart McCloskey and James Hume retain their places in the centre, while Zac Ward comes in on the wing while Jacob Stockdale moves to full-back and Werner Kok completes the back three.
Harry Sheridan has returned from suspension to take his place on the bench, while center Jude Postlethwaite is also named after suffering a hand injury against Edinburgh in March.
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Ronan O’Gara has made three changes to his La Rochelle team, which beat Newcastle Red Bulls 26-18 in the round of 16.
La Rochelle is without some key players, including captain Gregory Alldritt, Australian second row Will Skelton, defender Levani Botia and winger Davit Niniashvili.
Ulster: Jacob Stockdale; Werner Kok James Hume, Stuart McCloskey; Zac neighborhood; Jack Murphy, Nathan Doak; Angus Bell, Tom Stewart, Tom O’Toole; Iain Henderson, Cormac Izuchukwu; David McCann, Nick Timoney, Juarno Augustus.
Replacements: James McCormick, Sam Crean, Scott Wilson, Harry Sheridan, Bryn Ward, Conor McKee, Jake Flannery, Jude Postlethwaite.
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La Rochelle: Ihaia West; Ugo Pacome; Ulupano Seuteni, Adrien Seguret; Hoani Bosmorin; Diego Jurd, Tomás Berjón (captain); Louis Penverne, Gabin Garault, Karl Sorin; Thomas Lavault, Aleksandre Kuntelia; Edouard Richer, Kirill Fraindt, Lucas Andjissermatchi.
Replacements: Tolu Latu, Christian Luaki, Joel Sclavi, Alexandre Kaddouri, Nikolozi Sutidze, Judicael Cancoriet, Sacha Elissalde, Nolhann Couillaud.