Warren Gatland will wield the axe in selection if the British and Irish Lions do not cut out their indiscipline, Graham Rowntree has warned.
The Lions edged past 14-man New Zealand 24-21 in Wellington on Saturday night to square the three-Test series at one win apiece.
The All Blacks had to do without Sonny Bill Williams for almost an hour after the Blues centre was sent off for a head-high shoulder-charge tackle on Anthony Watson.
The Lions were almost hamstrung by conceding 13 penalties at the Westpac Stadium though, leaving assistant coach Rowntree to predict a lengthy inquest on discipline in the build-up to Saturday's series decider in Auckland.
"We've got to sort it out, as coaches we've got to show the players," said Rowntree of the Lions' second Test indiscipline.
"We show them every day. We sit there and show them that we can't be doing this.
"It's all about what you do under fatigue in the heat of the battle.
"All we can do is keep reiterating that to the players.
"You've got to sit down and look at it in the cold light of day.
"We can't lose a Test series on the back of some stupid penalties. That would be unacceptable.
"How would you live with that for the rest of your life?"
Asked if the second Test indiscipline could lead to selection changes for the series decider at Eden Park, Rowntree replied: "Potentially, if that's what it takes.
"Because I think Gats has shown he's not afraid to do that.
"We'll just be very frank about that with the players. The pictures are undeniable, some of them."
The Lions now head to Queenstown to recuperate after two bruising Test matches, with Rowntree backing that decision.
Gatland's men must end New Zealand's 39-match unbeaten streak at Eden Park to claim just the Lions' second-ever Test series win in New Zealand.
The Lions fuelled the underdog fire to edge past the All Blacks in the second Test as they squared the series after admitting being outmuscled in their 30-15 first Test defeat.
But now Rowntree insists the Lions can raise their levels again - and that their best rugby is yet to come.
"We're not playing at our best yet, there's so much more left in us," said Rowntree. "That will drive us on."
Asked how the Lions summon the same mental fight without the underdogs tag, Rowntree continued: "Because there's a series in the balance.
"How many of these guys have won a Lions series in New Zealand? And what excites the guys is that there's more to come in our game.
"After the first Test they were down, hurting. But now they've had a taste of it and they want to get the job done.
"So let's raise our game again and get into it."
The Lions could be without Sean O'Brien for the series decider after the Ireland flanker was cited for allegedly striking Waisake Naholo in the second Test.
Rowntree admitted the Leinster back-rower has made the Lions' power game tick in New Zealand - but backed the squad to cope if he missed the final Test.
"We'll deal with that as and when," said Rowntree.
"We've got a class group of back rowers and I'd have no qualms about anyone else stepping up.
"Sean had an outstanding game carrying the ball for us on Saturday.
"He's the barometer of our energy and aggression in the game; his ball pressure, his tackling, his carrying. He's been outstanding."