Carlton coach Brett Ratten is thinking about sending some of his forwards into defence, but it has nothing to do with tanking AFL games through questionable positional moves.

The Blues are desperate to bolster their backline given it has resembled a revolving door of late and because key defender Michael Jamison's season might be over due to a groin problem.

Jamison will undergo assessment on Friday that should determine the extent of the problem that has kept him out of the past three games, but Ratten conceded the 23-year-old may not play again this season.

So with a finals berth still to be secured, Ratten said the Blues (seventh) had to consider trying someone else in the backline in tough upcoming games against Geelong on Friday night at the MCG, Port Adelaide (round 20) and Adelaide (round 22).

"We've been that up-and-down through the year with losing (Paul) Bower through games, (Bret) Thornton had a hamstring there for a while, (Mark) Austin has missed games, we've used (Adam) Hartlett and (Joe) Anderson," Ratten said on Tuesday.

"We've used 37 players and probably a fair few through that defensive area.

"Sometimes through adversity or opportunity you find out about other people.

"Maybe we have to play a forward back or do something a little bit radical to see if we can find something."

Carlton's lack of key-position presence is not limited to defence, as Ratten would also like another marking target in attack to ease the reliance on full-forward Brendan Fevola.

But rucks Robert Warnock and Sam Jacobs, along with the fit-again Simon Wiggins, are not ready to be promoted from the VFL.

"It would be just great to have that opportunity," Ratten said.

"When you sit around the selection table, just to open that discussion to say `Is it the time now to (have) one of these talls in that front 50 to give Brendan a bit of a help down there with the high balls?'"

Matching Geelong will require a significant turnaround in Carlton's form and history, as the average losing margin in their past five defeats to the Cats is 65 points.

Ratten rejected suggestions the Cats were vulnerable given they also have defenders sidelined and put Carlton's emphasis on reducing the amount of Geelong possessions.

"They always get 400-plus possessions, maybe if we can reduce that and have the ball in our hands a little bit more that might be our window of opportunity," he said.

"That might be the tale of the whole game, if we can get enough ball and supply into that front 50."

Ratten refused to be brought into the focus on tanking even though in 2007 the Blues gained a priority pick in the national draft (used on ruckman Matthew Kreuzer) on top of selection three, which was traded to West Coast for Chris Judd.

"It's not the place to be saying they shouldn't have it in or they should, that's the system," Ratten said of the priority picks.

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