Geelong forward Ryan Gamble could be the beneficiary of Paul Chapman's injury blow, with the Cats forced to make at least two changes for Friday night's AFL preliminary final.

Chapman was ruled out of playing against the Western Bulldogs because of a hamstring injury sustained early in the qualifying final win over St Kilda.

With young midfielder Brent Prismall having ruptured his ACL in the same match, the door to the side has opened for at least two of a group that includes Gamble, James Kelly, David Wojcinski and Shannon Byrnes.

"We're really pleased that they're difficult (choices)," Cats football manager Neil Balme said.

"The difficulty is this week you can only pick 22 and we've got more than 22 that we want to pick. It's the best possible position to be in. So if we complain about that we're hard to please."

The fact that it is a Friday night match worked against Chapman, who has had recurring hamstring problems this year.

The tough forward is likely to be ready to return for the grand final, should Geelong beat the `Dogs.

Midfielder Kelly, who has not played since round 20 with a quadriceps injury, looms as the most likely replacement for Prismall.

Gamble can also mount a strong case for taking Chapman's spot in the Geelong line-up.

The hard-working forward has scored at least one goal in 12 of the 13 matches he has played this year.

He has the combination of marking ability and ground level and tackling skills that seem best suited to replace Chapman's loss.

Speedster Byrnes is also in contention to fill the small forward role.

Gamble and Byrnes were the two players dropped when Max Rooke and Andrew Mackie returned from suspension and injury respectively for the Cats' first final.

Running defender Wojcinski, who was a regular before injuring his Achilles tendon in July, could also slot into the side given the Bulldogs' wealth of small forwards.

But match fitness could work against him, given he has not played a senior game in two months.

He played the final two home and away rounds in the VFL, but the Geelong reserves side's failure to make the finals means the last of those was on August 30.

"He would have preferred to have played to get the conditioning, but he has done quite a bit of work, so it hasn't hurt him that much," Balme said.

The three other clubs involved in this weekend's preliminary finals also face some selection posers.

The Bulldogs' biggest question mark is over gun midfielder Adam Cooney, suffering from knee soreness and illness.

While the club insisted earlier in the week that he will play against the Cats, his form at training on Thursday is likely to give a clearer picture of his condition, after he failed to front on Tuesday.

Hawthorn and St Kilda also have their concerns ahead of their clash on Saturday night.

Hawks midfielder Chance Bateman will be assessed by the club on Wednesday after rolling his ankle on Tuesday.

The club is adamant key defender Trent Croad, whose presence will be vital against Saints tall targets Nick Riewoldt and Justin Koschitzke, will play, despite questions over his recovery from a bruised foot.

The Saints' biggest issue is whether to gamble on courageous midfielder Luke Ball, who will get a chance to demonstrate his recovery from a hamstring injury on Thursday.

The match committee then needs to decide whether he has the fitness to be rushed back into the team, despite last playing almost seven weeks ago.

Vice-captain Lenny Hayes, who had back spasms ahead of the Saints' win over Collingwood, will also be under the spotlight at training on Thursday, after failing to train on Tuesday.

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