Brendan Macken, who has scored three tries in the competition so far this year, again partners Collie O'Shea in the centre with Andrew Conway forming an exciting back-three alongside Darren Hudson and David Kearney.
Jack McGrath starts in the front row alongside Aaron Dundon and Jamie Hagan with Ruddock linking up with Jordi Murphy and Leo Auva'a in the back row.
Auva'a, who helped Old Belvedere win the Ulster Bank League title last season, has scored three tries in nine RaboDirect PRO12 games so far this year.
LEINSTER 'A' (v Llanelli): David Kearney; Darren Hudson, Brendan Macken, Collie O'Shea, Andrew Conway; Noel Reid, John Cooney; Jack McGrath, Aaron Dundon, Jamie Hagan, Ben Marshall, Mark Flanagan, Ciaran Ruddock (capt), Jordi Murphy, Leo Auva'a.
Replacements: Tom Sexton, Jack O'Connell, Jordan Coghlan, Conor Gilsenan, Luke McGrath, Cathal Marsh, Andrew Boyle.