Ill-discipline Waratahs' downfall?

Sydney - Ill-discipline is threatening to scupper the Waratahs' Super Rugby title defence, with Wallabies back Rob Horne set to miss the rest of the regular season after being handed a three-week ban.

Wing Horne will join suspended hooker Tolu Latu and Wallabies lock Will Skelton on the sidelines for the penultimate-round crunch match against the Cheetahs in Bloemfontein this weekend after committing a needless lifting tackle in Saturday's loss to the Lions.

Though Skelton will return for the final regular season match against the Reds, Latu and Horne will remain out until at least the second week of the playoffs, if the Waratahs make it that far.

With the team's playing stocks already stretched thin, Horne's sin-binning for the tackle helped the Lions to a half-time lead.

The Sydney side's second yellow card to back-row enforcer Jacques Potgieter shortly after the break all but killed off their chances of reeling in the home side.

The loss left the Waratahs clinging to top spot in the Australian conference but equal on 42 points with the second-placed Brumbies.

Another slip-up against the Cheetahs could prove fatal for their season.

"We need to stay positive and play our game," captain Dave Dennis told Australian media in South Africa. "Our destiny is still very much in our own hands on the ladder.

"There's a chance we could win two games and still not finish top if the Brumbies get the results but we're not focused on that."