Caoimhin Kelleher, Conor Masterson, Neil Farrugia, Michael Obafemi and Trevor Clarke have all been ruled out of the Armenia match.
West Ham United striker Anthony Scully has received his first call-up to the U-21 squad whilst Gavin Bazunu, Simon Power and Kameron Ledwidge all come back into the squad.
Corey O'Keefe, who is currently on loan at Macclesfield Town from Birmingham City, has also received his first U-21 call-up.
The squad trained in London this afternoon before tomorrow's trip to Yerevan ahead of the qualifier against Armenia on Thursday, November 14.
Republic of Ireland U-21 squad
Goalkeepers: Gavin Bazunu (Manchester City), Conor Kearns (UCD AFC).
Defenders: Thomas O'Connor (Gillingham, on loan from Southampton), Danny McNamara (Newport County, on loan from Millwall), Dara O'Shea (West Bromwich Albion), Liam Scales (UCD AFC), Nathan Collins (Stoke City), Corey O'Keefe (Macclesfield Town, on loan from Birmingham City), Kameron Ledwidge (Southampton).
Midfielders: Jason Knight (Derby County), Conor Coventry (West Ham United), Jack Taylor (Barnet), Jack Clarke (Aston Villa), Connor Ronan (DAC Dunajská Streda, on loan from Wolverhampton Wanderers), Dan Mandroiu (Bohemians).
Wingers: Zack Elbouzedi (Waterford), Gavin Kilkenny (AFC Bournemouth), Danny Grant (Bohemians), Simon Power (Ross County).
Forwards: Adam Idah (Norwich City), Aidan Keena (Hearts), Anthony Scully (West Ham United).