Brady has suffered back spasms while Walters has an achilles injury.
In better news Robbie Keane trained with the rest of the players.
The first group match is against Sweden next Monday.
In other Euro 2016 injury news, Northern Ireland manager Michael O'Neill says Kyle Lafferty's groin injury is not serious.
The former Norwich forward limped out of training this morning but O'Neill has allayed fears that he is a risk for the tournament.
Lafferty was Northern Ireland's top scorer in qualifying with seven goals.
In Women's soccer, Ireland are in action this evening as they host Montenegro in a Euro 2017 qualifier.
Kick off in Tallaght is at 7.
