Australia and New Zealand have both utilised virtually their whole 24-man squads in their opening two games, while for England, Zak Hardaker, Michael McIlorum, Liam Farrell and Rob Burrow are yet to see any game time.
McNamara said: “It is very difficult selecting a 17 to go out on the field at this time, because they are all very good players.
“We’re in a completely different position to some of the other teams. We have to make sure we navigate the best route to being successful, and if that means some players miss out then that’s the case.
“I’m certainly not basing my selection on making sure everyone’s feeling nice and fluffy because they’ve had a game, and the players understand that.
“They understand that we need every member of the group to be fully committed to the cause for us to achieve success, and sometimes that means not playing.”
He also praised the impact of returning loose forward Sean O’Loughlin and back-rower Brett Ferres, who starred down England‘s left-hand side having initially not made the 24-man cut for the tournament.