Essendon forward Irving Mosquito has walked away from the AFL at the age of 21 after losing the motivation to get back to the highest level.

Mosquito tore the ACL in his left knee in round 16 last year, and he was granted an absence of leave from the Bombers in May to return to his hometown of Halls Creek.

The speedy goalsneak has spent the past few months considering his future, and he has decided not to return to AFL ranks.

"It was a pretty tough decision to come to, and I had to weigh up whether I could commit to a full 12-month recovery program to get my knee right," Mosquito said.

"In the end, I realised I didn't have the passion that was required to get back so it's the right time to consider life away from football.

"The club has been great with their support of me and my family, I can't thank them enough.

"I will miss my teammates and being at the club every day. I wish the boys well for next season, I'll always love this club."

Mosquito, the No.38 pick in the 2018 national draft, made his AFL debut in the round 13 Dreamtime clash against Richmond last year.

He booted two goals in that match to showcase his potential, but he added just three more games before suffering the serious knee injury.

Essendon also announced that Ned Cahill and Lachie Johnson won't be offered new contracts for next year.