When Michael Hartley was delisted by Collingwood after two seasons on the rookie list at the end of 2013, the defender had given up on playing in the AFL again. "I thought I was definitely done," he said.

His stint at the Magpies was riddled by injuries (he was limited to five VFL matches in two years), and the hopes he had about establishing himself at the top level had faded, to the point where he was glad to leave Collingwood.

"It was sort of a blessing to be delisted. I was happy to get out of there, grow up a bit, get the body right and then maybe try again," he told AFL.com.au.

Fast forward and Hartley was a key member of Essendon's defence that stood firm last week against Adelaide and helped the Bombers to a come-from-behind win over the Crows.

Hartley was happy with how he handled that frantic final term, helping to repel from the back half. But what makes the 24-year-old most satisfied is his ability to take his second chance at an AFL career.

After his time at Collingwood, it was Hartley's father who advised him to stay in Victoria instead of heading home to Penrith in New South Wales. He signed with Coburg in the VFL, and took on a labouring job in his first season there.

In his second, he was "a maintenance man" at a hospital in Melbourne's northern suburbs, combining his work with training at night but also winning the club's best and fairest and making the VFL team of the year.

He looks back on his time at the Magpies as a reality check that he needed.

"Coming out of school, I thought I was going to get drafted and be the king of the world sort of thing, but it was a massive smack in the face to be honest. I was not mature enough, or ready for moving away from home or anything like that," he said.

"It's amazing how much I matured in that two years I was out of a club. With that experience I now know how hard it is to work all day and then go to training. When I was at Collingwood I took being in the AFL for granted, so now that I'm back I want to make sure I keep it."

Essendon selected Hartley with pick 68 in the 2015 NAB AFL Draft and he played 19 games in his first season with the club, filling in as the Bombers lost most of their senior players to season-long bans, including key defenders Michael Hurley and Cale Hooker.

When Hurley and Co. returned last season, Hartley's role changed and he found it difficult to hold down his spot, being left out of the side at times. He still played 18 games, including the Bombers' elimination final against Sydney, but wants to expand his game this season.

"In 2016 I was just trying to survive. I was playing on some good players and big fellas and it was coming in pretty hot and heavy at times," he said.

"But I was pretty lucky to get the opportunities I did and play most of the games, which was good. Last year I found it a bit hard, with the guys coming back, I had to play a bit differently and I got dropped a couple of times which wasn't the best.

"But this year I thought, 'I've done my two years as an apprenticeship, and this year I've got to step up a bit and get a bit more of the footy'. I want to use my kicking a bit more and be a bit more attacking."

Hartley will get more opportunities to do that with intercepting Bombers defender Martin Gleeson to miss half of the season, but knows there is still competition for places in Essendon's back half alongside Hurley, Mitch Brown and Patrick Ambrose.

He is out of contract at the end of the season but determined to show his worth this year. "I love Essendon and I'd love to stay at Essendon if they'd have me," he said. "Hopefully I can have a good year and see what happens."