But it has been enough to convince Voss that the classy utility is finally ready to step up to the next level for the Lions.
After admitting the club had to stop relying on Simon Black and Jonathan Brown in 2009, Brennan backed up his intent with a stand-out performance in the Lions' NAB Cup win over St Kilda at the Gold Coast on Saturday night.
His 21 possessions proved crucial as he combined with fellow old head Travis Johnstone (27 disposals) to steer a young Lions past the NAB Cup defending champions, giving Voss a perfect start to his coaching career.
Brennan has worn the "X factor" tag since his 2003 AFL debut.
But the dreaded "mercurial" and "enigmatic" badges have also never been far away due to his hot and cold performances.
Consistency, it seems, is no longer a problem for Brennan after a 2008 season in which he played in all 22 senior matches for the first time and averaged a career-best 18 disposals.
However, Voss admits there are some things about the Northern Territorian that will never change.
"You'd look at Jared in the past and he'd have this laconic look about him - well, he's never going to get rid of that," Voss laughed.
"But we have spoken to him about his consistency in the way that he trains and his application of that has been fantastic.
"He's really lifted his training levels."
Voss said Brennan had embraced extra responsibility in the pre-season - and hoped it would help take his game to "the next level".
Brownlow Medallist Black (broken wrist) has been ruled out of the NAB Cup competition and there is a question mark over Brown's availability in the pre-season.
"I don't think it is any fluke that you can translate that (training ethic onto the playing field)," Voss said of Brennan's impressive start to 2009.
"So let's hope that Jared can take that step up to the next level.
"We sure hope he can. He's got some added responsibility when Simon Black isn't there as well as Brown.
"Some of the main leaders weren't there (against the Saints) so seeing him step up was really good."
Voss said Joel Patfull would be among "three or four" players to return for a beefed up Lions in their NAB Cup quarter-final against Essendon on Telstra Dome on February 27.
