Neither player has recovered sufficiently to be considered available for selection for the upcoming games on the tour.
Uncapped Leinster hooker John Fogarty has been called into the squad to replace Best, while another uncapped player, Ulster lock Ed O'Donoghue, comes on board to take O'Connell's place.
The inclusion of Fogarty and O'Donoghue brings the number of uncapped players in the 33-man squad to five.
Declan Kidney's men will assemble in Limerick over the weekend and begin the tour with a game against the Barbarians at Thomond Park next Friday.
They will then fly out for a mouth-watering meeting with New Zealand in New Plymouth on Saturday, June 12.
The New Zealand Maori team is the next opposition for Ireland in Rotorua on Friday, June 18 as part of the Maoris' centenary celebrations.
The final game of the tour will see Ireland playing their 2011 Rugby World Cup Pool C opponents Australia in Brisbane on Saturday, June 26.
IRELAND Squad (2010 Summer Tour, June 4-June 26):
Backs (15) -
Tommy Bowe (Ospreys)
Gordon D'Arcy (Lansdowne/Leinster)
Keith Earls (Young Munster/Munster)
Shane Horgan (Boyne/Leinster)
Rob Kearney (UCD/Leinster)
Fergus McFadden (Old Belvedere/Leinster)*
Geordan Murphy (Leicester Tigers)
Brian O'Driscoll (UCD/Leinster)
Ronan O'Gara (Cork Constitution/Munster)
Tomas O'Leary (Dolphin/Munster)
Eoin Reddan (Lansdowne/Leinster)
Jonathan Sexton (St. Mary's College/Leinster)
Peter Stringer (Shannon/Munster)
Andrew Trimble (Ballymena/Ulster)
Forwards (18) -
Tony Buckley (Shannon/Munster)
Tom Court (Malone/Ulster)
Sean Cronin (Buccaneers/Connacht)
Jerry Flannery (Shannon/Munster)
John Fogarty (De La Salle Palmerston/Leinster)*
John Hayes (Bruff/Munster)
Cian Healy (Clontarf/Leinster)
Jamie Heaslip (Naas/Leinster)
Chris Henry (Ballymena/Ulster)*
Marcus Horan (Shannon/Munster)
Shane Jennings (St. Mary's College/Leinster)
Kevin McLaughlin (St. Mary's College/Leinster)
John Muldoon (Galwegians/Connacht)
Donncha O'Callaghan (Cork Constitution/Munster)
Mick O'Driscoll (Cork Constitution/Munster)
Ed O'Donoghue (Ballynahinch/Ulster)*
Dan Tuohy (Ballymena/Ulster)*
David Wallace (Garryowen/Munster)
* Denotes uncapped player
Summer Tour Match Schedule:
Friday, June 4: Barbarians v Ireland XV, Thomond Park, 7.45pm
Saturday, June 12: New Zealand v Ireland, Yarrow Stadium, New Plymouth, 7.35pm (8.35am Irish time)
Friday, June 18: New Zealand Maori v Ireland XV, International Stadium, Rotorua, 7.35pm (8.35am Irish time)
Saturday, June 26: Australia v Ireland, Suncorp Stadium, Brisbane, 8pm (11am Irish time)