12 Dec, 14:42
Prop Cian Healy is expected to miss the start of the 2014 RBS 6 Nations after undergoing surgery on his injured ankle on Wednesday.
The 20-year-old Leader, who hails from Galway, made his first senior appearance away to the Ospreys this time last year.
Commenting on the team selection, head coach Pat Lam said: "It's been a pretty disruptive week with injuries and we've lost more players with none coming back into the frame. So once again, we've had to dig deep into our resources
"With James and Danie injured in the backs, we've lost our cover at outside centre. And so young Darragh Leader comes on to the bench after impressing for the Eagles last weekend. He's been a big part of our training squad in recent weeks.
"Up front, Mata replaces Andrew Browne at six. Browney was unable to train fully this week due to a few knocks he picked up in the last game.
"But thankfully, with all the injuries we have to the back row, he recovered sufficiently to take his place on the bench.
"Dave Heffernan comes in as cover for hooker and this is a huge opportunity for him to make his mark."
The Connacht boss added: "Coming up against Leinster at the RDS - it doesn't get much bigger than that. The current Rabo champions, they've been consistently the best team in Europe for the last number of years.
"Full of internationals, we know their players will be out to stake a claim ahead of the November series. We know what we're up against.
"But these are the type of games you relish and we can't wait for the challenge. We have trained well on the back of a good win in the Heineken Cup and of course we have a plan to execute in order to give us the best opportunity to beat this team."
CONNACHT (v Leinster): Gavin Duffy; Tiernan O'Halloran, Robbie Henshaw, Craig Ronaldson, Matt Healy; Dan Parks, Kieran Marmion; Brett Wilkinson, Sean Henry, Rodney Ah You, Michael Swift (capt), Craig Clarke, Mata Fifita, Jake Heenan, George Naoupu.
Replacements: David Heffernan, JP Cooney, Ronan Loughney, Aly Muldowney, Andrew Browne, Paul O'Donohoe, Darragh Leader, Fionn Carr.