PORT Adelaide will be without ruckman Matthew Lobbe for the next three months with a serious knee injury.

Scans on Tuesday revealed that Lobbe had ruptured the posterior cruciate ligament in his knee in the SANFL last weekend.

Lobbe left the ground during the second quarter of Port Adelaide's SANFL match against Sturt.

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The Power's head of high performance, Darren Burgess, said Lobbe wouldn't have to have surgery.

"Really disappointing news for 'Lobes', the scans show a full rupture of the PCL, which will keep him out for around 12 weeks,'' Burgess said.

"The timeframes for recovery are pretty similar whether he has surgery or not.

"It's a fairly standard rehab program that he'll do, he'll be in a knee brace for about six weeks and will commence running in six to seven weeks.''

The Power is hopeful Lobbe will return about round 18 to give himself enough time to regain match fitness ahead of the finals.

Lobbe, 27, was the Power's first-choice ruckman at the start of the season. 

He played the first five games before being dropped for last weekend's match with Richmond at the MCG.

Lobbe has played 89 games for the Power since he was taken at No.16 in the 2007 AFL draft.

His absence will place more responsibility on the young shoulders of 20-year-old Dougal Howard, who has done a serviceable job in his two games this season. 

Key forwards Charlie Dixon and Justin Westhoff will also spend time in the ruck.