"It was a massive decision to leave him out (of the original 31). James has been an outstanding servant to Canadian rugby, the highest points scorer. As I said to him at the time, the mix (of the squad) had gone past him, but be ready," Canada coach Kieran Crowley told reporters on Thursday.
"He announced his retirement but he said if the opportunity came up in the World Cup, he was available, and he's obviously been training and playing with (English club) Bedford."
Pritchard has played in three previous World Cups but the 36-year-old will have to wait before he can make it four after Crowley kept faith with Matt Evans at fullback and brought Harry Jones on to the bench as cover for Saturday's Pool D game against Italy in Leeds.
'Hard work behind the scenes helping Ireland become a force,' says Fryday
Underwood came off the bench in the 50-7 defeat by Ireland in their opening game but picked up a knee injury.
'Scotland performance really disappointed me', says Easson
Saracens march on as play-offs confirmed in Premier 15s