North Melbourne youngster Flynn Perez has been ruled out of this season after suffering another serious knee injury at training.

The promising Kangaroo, who underwent a knee reconstruction that saw him miss his 2019 NAB AFL Draft season, on Thursday underwent an arthroscope to assess the damage of his training incident earlier this week.

The club had been unsure of the extent of the injury but surgery found that Perez, 19, had ruptured the graft in his previously reconstructed knee, meaning it has needed repair and required a second full ACL reconstruction.

It is a shattering blow for the speedy Bendigo Pioneers product and the Roos, who had high hopes for Perez to develop further this year after he broke through to play the final three games of last season as a running defender.

"This is obviously devastating for Flynn being his second reconstruction," North Melbourne football boss Brady Rawlings said in a club statement.

"Flynn’s attitude has always been first class and we have no doubt that he will return in great shape and have a real impact for us in the years to come.

"He’s very much part of this club’s future and as we do with all our players, we’ll take a long-term approach to their physical and mental well-being."

Perez was selected with pick No.35 in the 2019 draft despite not playing a game all season, with the former junior soccer star catching the eye with his skills on both feet as a bottom-aged player.

He had been returning to full training having recently had a hamstring injury that curtailed his pre-season.