The Western Bulldogs have suffered two massive blows, with crucial key-position defenders Liam Jones and Tim O'Brien removed from Sunday afternoon's clash with North Melbourne after respective injuries.

The 32-year-old Jones, who suffered an apparent forearm injury after receiving an inadvertent kick by Roo Paul Curtis, was substituted out of the game and replaced by Lachlan McNeil just ten minutes into the bout.

Jones was officially ruled out of the contest briefly after he was assisted into the rooms by the Bulldogs' medical team.

It's a devastating loss for the Bulldogs, as the ex-Blue had been playing in All-Australian form after integrating himself into Luke Beveridge's backline this year.

Shortly after half-time, the Dogs' defensive situation worsened after fellow key backman O'Brien was ruled out of the game due to a hamstring ailment, forcing formidable key forward Aaron Naughton into defence to aid an undermanned unit.

The two absences leave the Dogs vulnerable in defence, with defender Alex Keath representing the Bulldogs' last remaining natural key defender, needing to shoulder a massive load in combating tall Roos Nick Larkey and Callum Coleman-Jones.