St Kilda have signed Shaun McKernan as an unrestricted free agent with the former Essendon tall joining a third AFL club.

McKernan was let go by the Bombers at the end of last season after 53 games across six seasons.

The 30-year-old forward-ruck previously played for Adelaide after debuting in 2009.

McKernan becomes St Kilda’s second addition in the off-season after securing Adelaide midfielder Brad Crouch on Wednesday.

But the Saints might not be done there, with Richmond youngster Jack Higgins, and potentially, out-of-favour Collingwood star Adam Treloar in their sights.

McKernan will provide support up forward for rising star Max King.

The trade period runs until Wednesday, but Friday is the final day of the free agency period.

The Western Bulldogs are expected to sign veteran Brisbane Lions ruckman Stefan Martin, who is without a contract nearing his 34th birthday.

Tim English looms as a future gun, but he needed more support this year and the Bulldogs were forced to use midfielder Josh Dunkley in the ruck at times, which frustrated the premiership player enough to request a trade to Essendon.