The Gold Coast utility was dropped twice by coach Guy McKenna and finished the year playing in the Suns' reserves team.
At the age of 28 and after 158 games for the Suns and Brisbane Lions, he'd simply lost the passion.
Brennan admits he became reclusive from his teammates and gave only "30 to 40 per cent" of the required effort to be an AFL player.
He said that while being dropped ahead of the round 22 win over Carlton hurt at the time, his mind was already on holidays.
Following the season, Brennan got right away from football - he didn't watch any finals - and spoke to family, friends and wife Sharai about his future.
"I wasn't sure whether I wanted to keep playing at the highest level," Brennan said. "That was the thing I had to get my head around.
"Whether I still had the passion to play. It was looking pretty grim there."
Despite having two years to run on his contract, Brennan said it was a close run thing.
He has three children aged six, four and two all wanting more time with dad.
But the player that has often been labelled lackadaisical and lazy wanted to buck that perception.
"If I did give it away, I'd probably regret it for the rest of my life," he said.
"I've still got a few good years left in me and if I gave up now it was probably the easy way out. I don't want to be known to take the easy way out."
"That's the thing that's driven me this pre-season, to give everything I've got in every aspect - training, off-field, on-field - and we'll see where that takes us."
And so far so good, with Brennan voted by his coaches and peers as the best performed player at the Suns' recent two-week altitude training camp in Arizona.
Not only has he come back running as well as ever, but also made a more conscious effort to be a leader around the young team.
"I think the biggest improvement is giving more back to the group," he said.
"My first year I was ok at that, but my second year I really faded away and didn't do much with the group, I didn't talk to many people in the group."
"I'm a really shy person so it's easy for me to withdraw and do that. It's about me getting out of my comfort zone and doing more of that.
"Every training session I've given it all, getting around the young guys as much as I can. Off field I've done everything I possibly could to get myself right for this next season."
"I thought if I'm going to have a crack I'm going to give it my all and see what happens at the end of it.
"We'll talk to you in a year's time and see how it turns out."
