Lehmann made it clear he would be picking teams based on performance and not reputation - with deeds from the past, both good and bad, to count for little.
That's good news for Warner who is suspended until the Ashes start in Nottingham and won't have played for a month.
But it's a stern warning for players struggling for form, like fast bowler Peter Siddle, who won't be given a free pass to the Ashes simply because of his proven track record as a leader.
Warner has been first man to training since he was banned for drunkenly punching England rival Joe Root in a Birmingham nightclub, as he fights to salvage his place in the team, most likely in a new role as a middle order batsman.
Lehmann said Warner's attitude has been good, and if it wasn't he wouldn't be in the picture.
"I don't know what's happened in the past so for me he's got to do that (bring a good attitude) full stop," he said.
"And he's not the only one, everyone in the squad's got to train that way.
"He's been the first there and last to leave, so I've been pretty happy with his preparation.
"(He starts) very much so with a clean slate. We can't control what's happened in the past."
Siddle has battled for rhythm so far in the UK, with underwhelming performances for Australia A and then for the Australians in their opening tour match against Somerset in Taunton.
Lehmann said he was happy with what Siddle showed in the second innings in Taunton and will make a decision about whether the quick needs another trundle in the tour match against Worcestershire starting on Tuesday.
Siddle has proven himself as a warrior for the Australian attack, but with a talented cartel of six fast bowlers vying for spots, Lehmann says he can't completely trust the 28-year-old to play within himself until the Ashes arrives.
"Yes and no. We want him to bowl well each and every time, whether it's a tour game or a Test match, and he knows that," Lehmann said.
"The main thing for him is making sure he's ready to go. Bowlers are a different species at the best of times, mentally and physically. But for me it's a case of making sure they play the best they can each and every time."
Australia's Test batting order should become clearer when the team is announced for the Worcester match.
Captain Michael Clarke will get another chance to spend time in the middle and test his back, while Shane Watson will open the batting and bowl.
Squad members who didn't get a run in Taunton will play - with Chris Rogers to come into the mix in the top order, Steve Smith to bat in the middle and fast bowlers Ryan Harris and Jackson Bird to get their opportunity to impress.
James Pattinson will be rested after taking seven wickets against Somerset.Possible Australian team: Shane Watson, Chris Rogers, Usman Khawaja, Michael Clarke (capt), Phil Hughes, Steve Smith, Matt Wade, Peter Siddle, Ryan Harris, Jackson Bird, Nathan Lyon.