Lonergan, 30, is contracted with Geelong to the end of 2015, but AFL.com.au understands the Bulldogs have expressed their interest in trading for the premiership defender.
Western Bulldogs coach Brendan McCartney was a development coach at Geelong during the first eight years of Lonergan's career (2003-2010).
Lonergan's former teammates Matthew Scarlett, Cameron Mooney, Joel Corey and Steven King are all on the Dogs' coaching panel as well.
The Bulldogs' approach to Lonergan follows their inquiry about Brisbane Lions key defender Daniel Merrett, who turns 30 in December, earlier this trade period.
Since Brian Lake's departure to the Hawks at the end of 2012, Jordan Roughead and the undersized Dale Morris (190cm) have shouldered most of the Bulldogs' key defensive responsibilities.
The addition of Lonergan, 198cm, or Merrett, 195cm, would ensure the Bulldogs were much better placed to counter opposition power forwards.
Lonergan has played 145 games with the Cats since debuting in 2005, and was a member of the 2011 premiership side and the losing 2008 Grand Final team.
He was also selected in the preliminary All Australian squad in 2012 and 2014.
