After losing last week's opener to Australia in Cardiff, victory at the John Smith's Stadium is paramount if the hosts are to progress from Group A.
"Everyone is available this week," McNamara told reporters. "We've got 24 really good players in our squad and some very good players who didn't play last week.
"It's very early in the week and we're still partly reviewing the game. The players will all train today and tomorrow. We've got some decisions to make.
"If we need to make some changes, we will do, but I won't be playing anybody just for the sake of it. It's about winning the tournament. We've got to find the best route for that."
Fiji beat Ireland in the group's other fixture on Monday.