NORTH Melbourne key defender Joel Tippett could be sidelined for up to six weeks after copping a knee to the back in a VFL practice match on Saturday.

Tippett suffered extensive bruising to his lower back and a fracture of the transverse process, a small bony projection off the side of his vertebrae, while playing for Werribee against Footscray.

"Joel reported immediate pain and spasms in his lower back," North director of football Geoff Walsh said.

Match preview: North Melbourne v Melbourne

"Things have now settled and he will have follow up scans as part of his treatment."

Despite the severity of the incident, Tippett has avoided surgery and the Roos are aiming to have the 197cm big man back within a month.

"The word 'fracture' is never a good one when it comes to injuries, but in Joel's case, it is not one that will interfere significantly with his conditioning or long term spinal function," Walsh said.

"There’s no need for surgery and our medical team is certainly aiming at getting him back in about four weeks."

Tippett, 27, has played seven games for the Roos in the past two seasons – including the first two in 2015 – but has fallen behind Robbie Tarrant and Scott Thompson in the pecking order for a key defensive post. 

The former rookie joins recruit Jed Anderson (hamstring tendon), Ed Vickers-Willis (shoulder) and Daniel Nielson (knee) on the Roos' injury list.