Hooker Ethienne Reynecke, who injured his calf in the closing stages of the Pool 3 opener, will be replaced by Adrian Flavin in the front row.
There are no changes to the back-line with David McSharry, who will earn his 20th cap for the province, and Eoin Griffin continuing their centre partnership.
Griffin has shaken off an ankle injury to start as has teenage full-back Robbie Henshaw, who will be lining out against the English champions just seven months after captaining Athlone's Marist College to their first Connacht Schools Senior Cup title in 35 years.
On the bench, powerful prop Brett Wilkinson returns to the Connacht matchday squad from British & Irish Cup duty last week. He joins Jason Harris-Wright and Ronan Loughney as the front row replacements.
David Moore and Mata Fifita, both of whom were sprung from the bench against Zebre, are joined by Miah Nikora as the replacement backs.
Back rower John Muldoon, who was part of the Connacht side that claimed a famous 9-8 win over 'Quins last January, knows the visitors will be coming to Galway with revenge on their minds.
"We're looking forward to the game. It's a big, big challenge. Conor O'Shea will be coming over here and the biggest word they'll be using is 'revenge'," he told Newstalk's 'Off The Ball' programme.
"Because after beating Toulouse (in the pool stages last season) they were coming over here looking for a party and we kind of ruined it (their qualification hopes).
"Conor O'Shea is a very shrewd man and I'm sure he'll have a few plans up his sleeve. As will John Kingston, the former Galwegians coach. He's coming back to a familiar ground as well."
Tickets for the Sportsground tie are still available to purchase here, with Muldoon urging as many fans as possible to turn out and support Elwood's men.
"I believe there's 7,500 tickets sold. It's not a sell-out yet, there's still a few tickets available. But it should make for a great atmosphere," he added.
"We had 9,000 (in the ground) against Toulouse last year - bear in mind I've played in front of 200 or 300 people at the Sportground, so that was some day. We're hoping that we'll have something similar this weekend."
CONNACHT (v Harlequins): Robbie Henshaw; Tiernan O'Halloran, Eoin Griffin, David McSharry, Fetu'u Vainikolo; Dan Parks, Kieran Marmion; Denis Buckley, Adrian Flavin, Nathan White (capt), Michael Swift, Mike McCarthy, John Muldoon, Willie Faloon, George Naoupu.
Replacements: Jason Harris-Wright, Brett Wilkinson, Ronan Loughney, David Gannon, Johnny O'Connor, David Moore, Miah Nikora, Mata Fifita.