Johnson could be out for month

Michael Johnson on crutches in the Dockers changing room , speaking to teammate Ryan Crowley. Pic: Getty Images

Fremantle's All-Australian defender Michael Johnson could be out for a month after injuring his knee against Adelaide at Patersons Stadium today.

Johnson was substituted out with a right knee injury at half-time in the 40-point win over the Crows.

The 2013 All-Australian injured the leg in a slinging tackle late in the second term and spent the rest of the day on the bench nursing some crutches.

"He's got a slight medial (strain), maybe a grade one, maybe a grade two," coach Ross Lyon said. "That's anywhere from two to four weeks. So he won't play in the near term."