ESSENDON'S off-season search for ruck depth with its vacant list spot has reached late-blooming Norwood ruckman Henry Crauford.

And Collingwood has signed veteran defender Lynden Dunn, who is coming off a second successive knee reconstruction, to another one-year rookie deal via the pre-season supplemental selection period (SSP). 

Dunn, 32, has played 31 games for Collingwood since joining the club from Melbourne at the end of 2016 for a career total of 196 games. 

He hasn't played senior footy since round 15, 2018 when he ruptured the ACL in his left knee against Gold Coast. He then re-injured the same knee during the 2019 pre-season, wiping out the entire year. 

However, Dunn is nearing full fitness again and the Pies view him as valuable key defensive support for Darcy Moore and Jordan Roughead.  

Meanwhile, the Bombers were keen on basketball convert Nigel Lockyer since before Christmas but their wish for more ruck options might thwart the Northern Territorian's immediate AFL plans.

Essendon officials have until the SSP deadline on Friday to make a decision if they want to add a player before the season starts.

Recruit and ex-Giant and Blue Andrew Phillips has held the fort admirably during the pre-season games in No.1 big man Tom Bellchambers' knee-related absence.

Bellchambers is edging close to a return but anointed successor Sam Draper, who re-signed for four seasons last year without playing a senior game, is recovering from an ACL setback in May.

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The Bombers also spent a top-40 draft pick in November on athletic 202cm ruckman Nick Bryan from the Oakleigh Chargers in the NAB League.

However, Essendon is clearly anxious about where it stands.

Lockyer's been the one unlisted training constant at Tullamarine after an ankle injury delayed his arrival, with Crauford now the fourth footballer to earn a trial with Essendon.

Nathan Ireland, a 198cm defender from WAFL club Swan Districts, and Brynn Teakle, a 202cm East Fremantle ruckman, have already come and gone.

Lockyer and Teakle both played in the Bombers' Marsh Community Series victory over West Coast a fortnight ago.

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Crauford bolted onto recruiters' radar last year with an impressive SANFL campaign, albeit at reserves level because of the presence of premiership big man Sam Baulderstone.

The 22-year-old won the SANFL reserves' best and fairest award, averaging 16 disposals, five clearances and 27 hitouts on his way to winning a flag at that level.

Crauford stands 204cm tall and began training with Essendon late in the week to enter what appears to be a two-way race between him and Lockyer to win the last list spot.

The news follows the Bombers signing club great James Hird's son Tom as a Category B rookie this week.

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They already added to their list in the SSP, with Richmond premiership player Jacob Townsend signing in early December.

This vacancy owes to draftee Lachie Johnson's long-term knee injury.