Essendon must reach the AFL finals for two of the three defenders injured in Sunday night's win over St Kilda to play again this season.

The Bombers confirmed Patrick Ryder (knee) would miss the last two rounds and be unavailable should the Dons make an elimination final, while Courtenay Dempsey (hamstring) will miss games against Fremantle and Hawthorn.

Veteran fullback Dustin Fletcher (hamstring) was on Monday cleared of any serious injury, but could miss Sunday's clash against the Dockers at Subiaco Oval.

Ryder's absence means Essendon have again been hit hard in the ruck department as the key defender was forced into the centre earlier this season because David Hille (knee) and Jason Laycock (foot) were sidelined.

Ryder's injury means Tom Bellchambers, aged 20 and with just eight games' experience, is the Bombers' first-choice ruckman at the business end of the season, starting with a clash against Fremantle giant Aaron Sandilands.

The giant-killing win over the Saints put Essendon into the eight, but Matthew Knights' side cannot be assured of a final yet, as they are only half a game clear of ninth-placed Port Adelaide with two rounds left.

Ryder, Dempsey and Fletcher were all on the bench in the last quarter, when the Dons hung on to pip the previously-unbeaten Saints by two points.

Essendon football operations manager Paul Hamilton said the Bombers were relieved Ryder would not require surgery after he injured the muscle behind his knee.

"There was some concern that Paddy had sustained ligament damage so we are happy to learn his injury isn't anything more serious," Hamilton said.

"Unfortunately he will miss at least a couple of weeks as the muscle behind his knee heals which is obviously a blow for the side."

Dempsey suffered a hamstring strain, while Fletcher will be assessed during the week.

Essendon will also assess captain Matthew Lloyd (bruised heel) to see if he can return, along with midfielder Jason Winderlich (back).

Brent Stanton (hip) and Kyle Reimers (hamstring tightness) are expected to be available.

But half-back Bachar Houli will not play again this season because of a leg fracture he suffered in the round-19 draw with the Brisbane Lions.

Essendon midfielder Brent Prismall said despite their lowly status in 15th spot, Fremantle presented a real challenge given the Dons were wary of a letdown after achieving what no other side had this campaign.

"The big games that we have won we have let ourselves down a week later so that proves another challenge for us this week," Prismall said on Monday.

"We've been to Perth a couple of weeks ago so we know the ground and we didn't play too well over there (against West Coast in round 18), so we'll be looking to rectify that definitely."

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