Makeshift Wests Tigers halfback Robbie Farah is wary of Todd Carney's move to No.7 for the Sydney Roosters in Sunday's NRL clash at Campbelltown Stadium.

The Tigers and Roosters have both lost regular halfbacks for the clash, with Robert Lui (ankle) and Tim Moltzen (knee) sidelined for the home side and Mitchell Pearce (shoulder) out for Brian Smith's team.

Skipper Farah replaces youngster Blake Lazarus while Carney, who played all of his football in the halves before being shifted to fullback by Smith at the Roosters, slots in for Pearce after the NSW hopeful suffered a fracture in his shoulder during last weekend's loss to St George Illawarra.

"They don't lose too much even though Mitchell Pearce has probably been the form halfback of the comp," Farah said.

"It's a pretty good luxury when you can move Todd Carney into fullback and you've got (Anthony) Minichiello at fullback, so it's a pretty good combination they've still got going."

But Farah said he still expected Carney to have to find his feet in a new position at a new club.

"It's going to be another challenge with him, playing halfback for the first time at a new club so we're going to have to try and put as much pressure on him as we can," Farah said.

"If not, he's shown what he's capable of, he's been in great form."

"He's not a small bloke either, Toddy, he's well over 90 kilos so I don't think he's ever had any problems defensively."

Tigers coach Tim Sheens described last week's second half of the 26-18 loss to Penrith as the worst he'd seen in attack in his time at the club.

"Our losses the last two weeks have come from shooting ourselves in the foot, we haven't been completing our sets, stupid errors and silly penalties," Farah said.

"We've been starved of possession, so you're not going to win footy games when you do that.

"Last time we played them (in round two) they put 44 past us ... that was a pretty embarrassing loss for us that day, so we know what we're up against and we know that if we don't turn up it could be a similar scoreline."

The Tigers' back-up at hooker and halfback will be 26-year-old debutant Nathan Waters.

"He's not the quickest guy going around but when he gets out there he's going to give it his all and he's got a great competitive nature about him and he'll do a good job for us," Farah said.

The Tigers are looking down the barrel of three straight losses in what will be Sheens' 600th game as coach.

The Roosters will look to avoid back-to-back losses for the first time this year.

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