The Fremantle debt collectors are out in full force, and they want ruckman Zac Clarke to pay up over the next three weeks.

Clarke has been a big disappointment for the Dockers this season, with his strong start to the year followed by a long lean spell.

In his past six games for the Dockers, Clarke has averaged just seven disposals and 13.5 hit-outs per game.

He has also been ineffective up forward, booting only two goals during that period, with his drop in form resulting in a long stint in the WAFL.

If it wasn’t for an untimely hamstring injury to fellow ruckman Jon Griffin, Clarke would have been overlooked for last week’s qualifying final win over Sydney.

Griffin hopes to be fit for next week’s preliminary final against either Hawthorn or Adelaide, but the Dockers may stick with Clarke given the 25-year-old’s potential.

However, coach Ross Lyon has made it clear in no uncertain terms that he wants the 88-game veteran to produce the goods if given the chance over the next few weeks.

“We’ve invested basically 100 games into Zac as a club, and it’s about returning investment,” Lyon told Perth radio station 6PR.

“This is the time of year we need a bit of payback. There’s plenty of upside in him. I thought he competed really well against Sydney.

“He’ll be better for the run. He went in with a bit of a sore knee, but he’s pulled up pretty well.

“He’s probably a little bit lucky because Jon Griffin was going well until he hurt himself. He’s grabbed his opportunity.”

Clarke tallied eight disposals, 11 hit-outs, and three marks in a steady showing against the Swans.

The Dockers entered that game with just one recognised spearhead – skipper Matthew Pavlich.

But 198cm forward Matt Taberner is a strong chance to earn a recall for the preliminary final after booting five goals in the WAFL last week.

Defender Luke McPharlin (calf) is in a race against time to prove his fitness after being a late withdrawal against Sydney.

Brownlow medal favourite Nat Fyfe (leg) and Pavlich (Achilles tendon) are considered certainties to play in the preliminary final despite their ongoing injury woes.

Tagger Ryan Crowley will be available for selection after serving his 12-month doping ban, but he’s almost certain to be overlooked.