A NEW AFL rule allowing clubs to sign previously listed players as Category A rookies will give Carlton until the eve of the 2019 season to replace injured co-captain Sam Docherty.

The Blues were dealt a significant blow on Monday, with Docherty expected to miss his second successive season after again rupturing the ACL on his troublesome left knee.

Previously, clubs couldn't replace players who had suffered season-ending injuries or who had unexpectedly retired after list lodgement deadlines had fallen.

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However, the AFL's recently introduced pre-season supplemental selection period (SSP) rules now enable clubs to replenish their lists with new signings through until March 15.

Carlton was among a host of clubs which already had one rookie spot available for an SSP signing after the trade and draft period, but can now move Docherty to its long-term injury list to create a second vacancy on its rookie list.

The rules give the Blues flexibility to potentially replace Docherty and have said they will explore the possibility of doing so in the future, though it's understood they are unlikely to make a call on signing any new players until after Christmas.

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"We left a list spot open that we can add to leading into the mid-year time," Carlton football boss Brad Lloyd told radio 3AW's Sportsday on Monday.

"We left that open to add a good quality player that's missed out on the draft previously, but with Sam's situation there are some long-term injury options and we can look down that path.

"(List managers) Stephen Silvagni, Mick Agresta and the rest of the team had already been looking at what was out there … so we'll have a look at that tomorrow and work out how to use our list to its full capacity."

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A number of retired or delisted players would be available to sign for Carlton under the new rules, including former Sydney defender Harry Marsh and ex-Fremantle utility Cam Sutcliffe.

Veteran defender Brendon Goddard is another who could come out of retirement, which he announced last week, should he get a call from Carlton.

Former player Jed Lamb had been training with Carlton in the hope of earning a place on its rookie list and would be available, while Northern Blues defender Mason Blakey is also eligible – having previously nominated for a draft – and was also training with the Blues.

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Another option could see the club wait for next year's newly introduced mid-season draft to recruit state league players, though details regarding its timing are yet to be confirmed.

Carlton has a number of internal options in order to replace Docherty in 2019, with young defender Tom Williamson set to return from a season on the sidelines due to a back injury.

The club also added to its defensive stocks with Nic Newman, Hugh Goddard and Ben Silvagni across the trade and draft period earlier in the year.