MELBOURNE draftee Christian Petracca's season-ending knee injury happened while performing a movement he had done "a thousand times" before. 

The 19-year-old ruptured the anterior cruciate ligament in his left knee at training in mid-February and had a traditional knee reconstruction the following week.

Petracca said he thought he had only sustained a minor injury after pushing off his teammate in a marking contest.

"It's pretty annoying because I've done that action probably a thousand times in basketball and football so it was just a once-off," Petracca told the club's website.

"After (the incident), I felt all right. I was running after it and thought it was a hyper-extension."

Petracca, who is no longer on crutches, said he was slowly beginning to strengthen his legs.

His rehabilitation program includes bike riding, swimming and frequenting the gym three days a week. 

"Rehab is quite lonely, there's only a few of us. There's only me and (Jack) Trengove (on long-term injuries) and a few others who are just short-term," Petracca said. 

The No.2 selection in last year's NAB AFL Draft said his next objective is to begin running.

"It's just all stepping stones really, you don't want to look at the big picture too soon, you want to gradually get there step by step," he said.

"The physios are pretty happy with my progress so far."

Although the 186cm on-baller has been ruled out for 2015, he said he is maintaining a positive attitude.

"It's a new journey, a new challenge in my life and I'm ready to accept it," he said.

Petracca said his prolonged absence would give him the opportunity to assist the Demons' recruiting team and gain an insight into opposition scouting.

"(National recruiting manager) Jason Taylor, I've been under his wing a little bit, he's taken me to a few TAC Cup games and (I've) watched a few players from there," he said.

In last year's NAB AFL Under-18 Championships, Petracca capped off his impressive carnival for Vic Metro by winning the Larke Medal as the best player of division one.