Niall O'Connor, who started Ulster's opening two league games, Hallett, Adam Larkin and Paddy Wallace will all be vying with Humphreys for the number 10 spot.
Del Fava played in two pool games for the Azzurri against Portugal and Scotland in recent weeks. The South African-born lock was involved in pre-season training with Ulster before he was called up for World Cup duty and takes Ryan Caldwell's place in the Ulster selection as the latter was not considered due to the red card he received against Edinburgh last week - Caldwell is due to attend a disciplinary hearing tomorrow evening.
The Edinburgh game left coach Ulster boss McCall frustrated as his side allowed Edinburgh build up too much of a lead during the 24-10 defeat at Murrayfield.
"It was a very disappointing display - we didn't wake up for half-an-hour. We played better in the second half but kept turning the ball over and we couldn't hold on to the ball long enough to score," McCall admitted.
"At this level if you make as many mistakes as we did, especially in crucial areas of the pitch, you don't deserve to win. We lacked composure. There was good build-up play to the 22 and then we tried to force passes."
An ankle injury has ruled flanker Kieron Dawson out of this weekend's trip to Wales, but full-back Bryn Cunningham (dead leg) and lock Matt McCullough (back) are in line for some involvement after recovering from their respective injuries.
In total, Ulster are missing 13 players due to injury or recovery from the World Cup. A number of Ulster's Ireland players, including Rory Best, Bryan Young, Stephen Ferris, Neil Best, Isaac Boss and Paddy Wallace, will hope to return to provincial duty over the coming weeks, while prop and former Ulster skipper Simon Best visited a cardiac specialist in Dublin today to weigh up his options after he was diagnosed with having an irregular heartbeat.
ULSTER Squad: Forwards - Justin Fitzpatrick, Declan Fitzpatrick, Tom Court, Nigel Brady, Matt Miles, Justin Harrison, Tim Barker, Carlo Del Fava, Matt McCullough, David Pollock, Neil McMillan, Roger Wilson (capt).
Backs - Paul Marshall, Kieran Campbell, Niall O'Connor, Adam Larkin, Kieran Hallett, Darren Cave, Tommy Bowe, Seamus Mallon, Simon Danielli, Mark McCrea, Mark Bartholomeusz, Bryn Cunningham.