Season-ending knee injuries to AFL stars Tom Liberatore and Eric Mackenzie have revived debate about the structure and timing of the pre-season.

The two reigning club champions were hurt in the weekend’s opening NAB Challenge matches.

Mackenzie tore an anterior cruciate ligament in West Coast’s match on Friday against Carlton.

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Liberatore did not last the first term of the Western Bulldogs’ game on Saturday against Richmond before suffering the same injury.

The two players will undergo season-ending knee reconstructions.

It has also emerged that Liberatore’s teammate Nathan Hrovat spent Saturday night in hospital after fracturing a rib against the Tigers.

Fellow Bulldog Will Minson said he wants further change to the pre-season structure.

Eric Mackenzie will now undergo season-ending knee reconstruction. Photo: Getty

In the last couple of years, the league has changed the pre-season matches between clubs from a knockout competition to a schedule of three matches per team.

“Definitely, there are lot of people who feel there is a better way that the pre-season can be structured,” Minson told Melbourne radio station SEN.

“The sheer fact that the off-season is longer than the in-season doesn’t seem to make much sense to me.”

This year’s AFL regular season will run from April 2 to October 3, or six months and one day.

If Minson had his way, players would not return for the pre-season until after Christmas.

“That would be the best outcome for me, because that sounds a lot better than starting six days a week in November,” he said.

“The point is, we want to play games of football and we want to play them for points.

“I know I was excited to play on the weekend because I was sick of playing against my teammates.”

Minson added Liberatore’s injury happened because of an innocuous incident.

“It’s the perfect storm as far as what every footballer dreads.

“It couldn’t have been a worse outcome for poor old Libba.

“There’s a fair bit of bad luck in it.”

-AAP