A DETERMINED Luke McDonald has promised to "work my arse off" during the off-season in a bid to ensure he doesn't have another "disappointing" year.

As forecast by AFL.com.au last Friday, McDonald has signed with the Roos until the end of the 2021 season.

McDonald, 23, said he thought he would be further advanced, having now played 94 games since being taken as the No. 8 pick in the 2013 NAB AFL Draft under the father-son rule.

"To be honest, personally, [I'm] pretty disappointed with how I've been going," McDonald told North Media.

"I probably haven't improved the way that I would have liked, but that's footy – you have your ups and downs."

McDonald played 22 games in 2017, primarily across the back line, averaging 21 possessions and 4.3 tackles per match, while this season his numbers are down to 18.7 touches and 2.3 tackles.

"I don't really have any excuses," said McDonald.

"Over the pre-season I'm just going to work my arse off and get in the best nick I can possibly be in, but I have played in a lot of different roles this year.

"[I've] played a bit in the backline, on the wing, even a few run-with roles in the midfield, so it's been sort of good being able to play everywhere but would be nice to settle downn but I suppose that's one of my strengths; being able to play wherever and I'm always happy to play wherever the team needs me.

"Without a doubt it's been awesome for my education to learn every role and know that I can play any position on the ground."

The son of Donald McDonald, who played 155 games for the Roos between 1982-1992, Luke was rapt to be at Arden Street for a further three years, and was confident the club will enjoy success during that period.

"I'm stoked to be here the next three years and hopefully longer… I absolutely love the club, as everyone probably knows; you know I've gone for the club ever since birth so [it's] awesome to wrap up another three years."