Damian Browne lines up alongside Devin Toner in the second row, while Jordi Murphy comes in for his first senior start after also coming off the bench against Glasgow Warriors.
The back-line is unchanged meaning Cillian Willis partners Ian Madigan at half-back. Eoin O'Malley again lines up alongside Luke Fitzgerald at centre with David Kearney, Fionn Carr and Isa Nacewa completing the back-three.
Prop Jamie Hagan, who started Leinster's opening three league games, said: "There's a lot expected when you play for Leinster and we are all determined to put last weekend's defeat to Glasgow Warriors behind us.
"It just wasn't good enough. When you come in on a Monday morning you know that you have to be prepared to hear some home truths, the lessons learned from last weekend. We're determined to meet this challenge head on."
LEINSTER (v Scarlets): Isa Nacewa; Fionn Carr, Eoin O'Malley, Luke Fitzgerald, David Kearney; Ian Madigan, Cillian Willis; Heinke van der Merwe, Richardt Strauss, Nathan White, Damian Browne, Devin Toner, Rhys Ruddock (capt), Jordi Murphy, Leo Auva'a.
Replacements: Jason Harris-Wright, Jack McGrath, Jamie Hagan, Mark Flanagan, Ciaran Ruddock, John Cooney, Brendan Macken, Darren Hudson.