A potential season-ending knee injury to powerful forward Wycliff Palu and fitness worries for other key players added further concerns for the Waratahs after their 20-13 loss to the Crusaders in a crucial Super 14 rugby contest in Christchurch on Saturday.

The Waratahs, who entered the round in top spot, slipped to third following their first loss in six games.

The Crusaders trailed 13-9 early in the second half, but inexorably worked their way back into an attritional contest which produced just one try for each side.

The seven-times Super title winners edged the visitors in the scrum and at the breakdown.

The Crusaders dominated territory and possession in the final quarter and scored the last 11 points to stretch their unbeaten run to six games.

They moved up to second on points differential above the Waratahs, who picked up a bonus point, with both teams four points behind the ladder-leading Bulls.

NSW coach Chris Hickey will have plenty of injury concerns over the Waratahs bye week, with Palu and three other key players, hooker Tatafu Polota-Nau (a shoulder), prop Benn Robinson (forearm), and five-eighth Daniel Halangahu (knee) all on the casualty list and expected to undergo scans on Monday.

Hickey said he wouldn't know until then whether any of the injured quartet could make the increasingly important April 24 showdown with the Brumbies, who are three points behind NSW with a game in hand.

"It looks like Cliffy might have done a cruciate injury, we won't know till probably Monday but if that's the case it will be his season gone," Hickey told AAP.

"Tatafu injured his shoulder and we won't know about that until he gets a scan, Benn got a direct blow on his forearm, which affects his grip strength and he will have to have a scan.

"They are probably the three big injuries we take out of it and Dan Halangahu has done a medial ligament."

Hickey was pleased with his team's defensive display, but conceded it was hard to beat a team like the Crusaders when they were starved of possession in the final quarter.

"I thought we played reasonably well when we could get our possession," Hickey said.

"In the last 15 to 20 minutes we didn't get possession and I think we defended particularly well, but eventually the weight of possession and that position on the field probably meant there was going to be a crack somewhere."

Crusaders five-eighth Dan Carter, who passed the Brumbies Stirling Mortlock to become the all-time leading Super pointscorer, kicked five penalties.

The home team iced their win with a 77th minute try to halfback Kahn Fotuali'i, who was sin-binned late in the first half for an illegal tackle on Waratahs inside centre Berrick Barnes.

Centres Barnes and Rob Horne, fullback Kurtley Beale and in form winger Drew Mitchell all looked dangerous for the Waratahs, particularly in the early minutes of each half.

NSW eked out a 13-9 lead after 51 minutes following arguably the most compelling passage of play in the year's tournament.

Horne scored off a stab kick from Halangahu after 29 phases of patient attack and gutsy defence.

Carter nudged the Crusaders ahead with two penalties and Fotuali'i rewarded the sustained pressure with the match-clinching try.

The first half produced just two penalties for each side.

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