COLLINGWOOD free agent Nathan Brown has become a target for North Melbourne.

The 27-year-old Brown would be a good fit for North Melbourne's defence, with 32-year-old Michael Firrito set to depart at the end of the season after a fine career with the Kangaroos.

Premiership defender Brown is understood to be a required player at the Magpies and is believed to have a contract offer to stay, but will assess his options during September.

With key defenders at the top four clubs going into finals including Sydney Swan Heath Grundy (30), Geelong's Tom Lonergan (32), Hawthorn's Josh Gibson (32) and 31-year-old Giant Joel Patfull, Brown shapes as a solid option for the Kangaroos.

A popular player at Collingwood, Brown has played 130 games and was part of the club's leadership group this season.

After a slow start to 2016, Brown showed good form in the back half of the year, and has been a durable performer in the past two seasons, finishing in the top 10 of the Magpies' best and fairest in 2015.

Brown told AFL.com.au in August he was continuing to improve with experience.

"They are parts of my game that I want to grow going forward in my career and I believe there is still room for that one-on-one contest that I love," he said.

He said at the time he was happy to wait before ramping up discussions about whether he would remain at the Magpies.

Collingwood is yet to contract free agent Jarryd Blair, while North Melbourne is yet to re-sign midfielder Daniel Wells.

Any move to recruit Brown could be complicated by Wells' decision.

If Wells decided to leave, then the club would have to weigh up the Brown decision given recruiting the Magpie could affect compensation it might receive for Wells.

North Melbourne will also be keen to hold on to its first round draft pick, with the club having had a first round pick every year for the past decade.

Collingwood's Travis Cloke requested a trade on Tuesday, while Dane Swan, Alan Toovey and Brent Macaffer retired last week.

North Melbourne plays an elimination final next Saturday night against Adelaide after falling from top spot to eighth in the final 13 rounds of the season.