Skipper Dave Dennis has warned his NSW Waratahs there can be no room for complacency as they walk the finals tightrope in Sunday's Super Rugby game against the Johannesburg-based Lions.

The Waratahs fell out of the top six for the first time all season after their weekend bye and will plummet further down the ladder if they fail to post back-to-back victories for the first time in 10 weeks.

"We've obviously had that run of win, loss, win, loss for the last couple of weeks and it is something we've talked about: putting that win, win back to back," Dennis said.

The Lions are 11th with virtually no hope of making the playoffs and Dennis on Tuesday admitted the Waratahs of old "would have taken them a bit easy".

But determined to build a new winning culture at the Tahs and after watching the Lions come within a point of hauling in the Dunedin-based Highlanders from 23-0 down last Saturday, Dennis promised that there'd be no disrespecting the South Africans.

"They should have won that match," Dennis said.

"Seeing what they've done over previous weeks definitely gives you an insight into what they're capable of. They're a strong attacking team."

Despite being out of finals contention, the Lions won four matches to sit third in the South African conference, above the Cheetahs and Stormers.

"Probably teams might have underestimated them a bit in terms of what they're capable of," Dennis said.

"They're nice and physical, they've got some strong ball carriers, they play quite wide and they can score points.

"So we're expecting a physical game to start with - most South African teams are physical - and also that threat of having to defend the whole field is going to be a good challenge for our defensive system.

"Obviously in our last outing, we let ourselves down in that area, conceding 30 points against the Hurricanes so it's something we've got to be better at."

With a rare Sunday game, the Waratahs will have waited 15 days between matches by the time they take to Allianz Stadium.

"You can look at the break and say it's too much and people could say you've had too much time off and your head's elsewhere," Dennis said.

"Or you can say it's been an opportunity to freshen up. It's been a tough slog for a while. We're in a good position. There'll be no excuses come Sunday not to put in a good performance.

With lock Jacques Potgieter carrying a leg injury, NSW coach Michael Cheika delayed naming his team until Thursday or Friday. - AAP