And the powerful 26-year-old, who had been playing for provincial based New Zealand side Taranaki, is now ready to feature in the match day 23 as Blues hunt a winning end to the pool stages of the cup.
"Isaia has been in with us for a week now and he will be involved in the game. Hopefully he will show a little of what he can do," said John.
"He has still got to get totally used to our patterns and the way we play, but he is keen to be involved and I'm looking forward to seeing him play. He will look to give us something extra.
"This period is important to us," added John. "We want to build confidence and we have some massive games left in the RaboDirect PRO12.
"It's a big opportunity for a number of the players to put their hands up for selection so there is plenty to play for.
"It's a tough assignment; Harlequins are a quality team with good players. But we will see how we go and hopefully it will be a good occasion and we will produce.
"We need those that didn't play last week to come in and get some game time before we play Munster. But injuries give opportunities and people have got to take them when they come."
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