HAWTHORN midfielder Beau Muston will miss the 2008 AFL home and away season after scans revealed on Monday that the youngster requires a third knee operation.

Muston, the Hawks’ second-round selection in the 2005 AFL Draft, injured his left knee in the opening term of Saturday night’s NAB Cup semi-final against Adelaide at AAMI Stadium.

Scans revealed the 21-year-old tore his anterior cruciate ligament, grafted in a previous operation two years ago.

He is expected to go under the knife in the next fortnight.

It’s a disappointing blow for Muston, who made steady progress in the VFL last year and was expected to make his senior debut in 2008.

He had reconstructive surgery in 2005 in his final year in the TAC Cup with the Murray Bushrangers.

He underwent further surgery shortly after, following a medical examination which showed signs the graft and screws had loosened.

Muston's manager Paul Connors said the promising midfielder had been all but assured of making his AFL debut in the Hawks' opening round match against Melbourne.

"He woke up Saturday morning and life was pretty good, he was 99 per cent sure of playing his first ever AFL game in round one against the Dees ... it's his 21st birthday and life's great," Connors told Melbourne sports radio station SEN.

"A few hours later it's turned around."

Connors said there had been little he could say to comfort Muston, despite pointing out other players, such as Richmond's Mark Coughlan and Carlton's Richard Hadley, who were playing after multiple reconstructions.

"As he said, (those recurrences) happened straight away, this has been a year-and-a-half of a full pre-season, a whole season of playing, another pre-season," he said.

Connors said it would be a tough road back emotionally.

"The players' association are a wonderful organisation, let's not take away from Hawthorn, it's a great club and he'll be surrounded by good people," he said.

"But there's going to be some ups and downs for Beau along the year I'm sure."

A Hawthorn Football Club statement said on Monday the young Hawk faces another period of rehabilitation “and the club will continue to support Muston in his quest to make a full recovery”.