Shamrock Rovers duo Graham Burke and Aaron McEneff are among four more players called up to the Republic of Ireland squad after the number of players ruled out from the original group rose to 13 today.
Former Under-21 player Jack Taylor of League 1 side Peterborough is also brought into the squad, while Troy Parrott has been promoted to the senior side from Jim Crawford's group.
Burke has two caps recorded under Martin O'Neill from 2018, scoring against USA in a friendly.
McEneff, a 25-year-old midfielder and outstanding for the Hoops this season, played underage football with Northern Ireland, but chose to play for the Republic of Ireland several years ago.
Adam Idah has withdrawn through injury. Matt Doherty and James McClean have tested positive for Covid-19.
Stephen Kenny is still awaiting his first win as Ireland manager and the coronavirus has contributed to his difficult introduction to senior international management.
A total of 13 players from the original squad named are unavailable to face Bulgaria, including the suspended Jeff Hendrick and Jayson Molumby.
Idah, Seamus Coleman, Enda Stevens, Aaron Connolly, Alan Browne, James McCarthy, Callum Robinson, John Egan and Harry Arter complete the dozen ruled out.
Republic of Ireland squad available on Wednesday as it stands
Goalkeepers: Darren Randolph (West Ham United), Caoimhín Kelleher (Liverpool), Mark Travers (AFC Bournemouth)
Defenders: Kevin Long (Burnley), Shane Duffy (Celtic), Dara O'Shea (West Bromwich Albion), Cyrus Christie (Nottingham Forest), Ciaran Clark (Newcastle United), Darragh Lenihan (Blackburn Rovers), Ryan Manning (Swansea City).
Midfielders: Conor Hourihane (Aston Villa), Robbie Brady (Burnley), Jack Byrne (Shamrock Rovers), Jason Knight (Derby County), Josh Cullen (Anderlecht), Aaron McEneff (Shamrock Rovers), Jack Taylor (Peterborough United).
Attackers: Graham Burke (Shamrock Rovers), James Collins (Luton Town), Ronan Curtis (Portsmouth), Callum O'Dowda (Bristol City), Daryl Horgan (Wycombe Wanderers), Sean Maguire (Preston North End), Troy Parrott (Millwall, on loan from Tottenham Hotspur).