Umaga's frustration probably stems from the fact that several of his top players have already been ruled out ahead of his team's first season in the Premiership after their promotion last year. They open their season on Thursday night with a match at Pukekohe against Wellington without hooker Mahonri Schwalger, who recently had knee surgery, and halfback Augustine Pulu and utility back Tim Nanai-Williams, who also need surgery on leg injuries.
Tupou, a former member of New Zealand's Under-20 squad, is a player with plenty of promise. At 1.96m tall, he can play blindside flanker, No8 or lock.
Blackadder said: "I can understand Tana's frustration there. A player like Jimmy would have been a key figure for Counties this season. It is just unfortunate that it turned out like it did."
Umaga said: "We've had our injury issues even before the season has started which is not helpful but I know we're not the only province to have that ... it just gives guys the opportunity and tests our depth which we've been working on for the last couple of years."
Compounding Umaga's problems is the fact that Wellington will include a forward pack containing an excellent tight five and a loose trio of Ardie Savea, Brad Shields and recently rejected All Black Victor Vito.
"It's not going to be easy for us, but we always knew it wouldn't be easy," said Umaga. "We love the challenge of trying to play against the bigger unions.
"Our guys have aspirations as well. If they're playing against All Blacks and future All Blacks it's the opportunity to play against the best of the best and that's what is so good about this competition."