Scans on Monday revealed that Collingwood defender Ben Johnson has not suffered any ligament damage to his right knee.

He did, however, suffer kneecap displacement.

As a result Johnson, who turned 29 today, is likely to be out of action for anywhere from 2-4 weeks.

Johnson sustained the injury during the second quarter of Saturday's one-point victory over Melbourne at the MCG.  He left the ground immediately and did not return to the field