FREMANTLE coach Justin Longmuir is confident ruck Sean Darcy can fast-track his adjustment to new ruck rules as the season starts, despite spending limited time this pre-season jumping at centre bounces. 

Meanwhile, the coach said he had short-term concerns around how centre bounces would be adjudicated under new rules but he was confident early teething problems would sort themselves out as players and umpires adjust. 

Darcy suffered a minor calf injury during match simulation in January and will play in a WAFL practice match on Saturday, rather than in the Dockers' AAMI Community Series clash against Adelaide, as the club manages his minutes. 

The big man completed a strong pre-season up until late January, but the timing of his injury has meant he was sidelined as the Dockers rucks increased their centre-bounce training. 

Longmuir said he was not concerned about the 27-year-old's ability to adjust to the new rules as he builds towards playing in the club's opener against Geelong on March 14.  

"Sean did a lot of work early in pre-season and he played a lot of match sim in the ruck, but early in pre-season we don't tend to jump a lot. We treat it like a ball-up," Longmuir told AFL.com.au. 

"We don't want our rucks jumping into each other at the start of January. We want to try and build that, so he's probably missed a fair chunk of that.

"It's not as though he's never jumped at centre bounce, so once he's back he'll be fast-tracked.

"I think even the rucks that got across the line and tried to nullify the opposition's jump, they'll find a way to make it to their advantage as well, so I'm not concerned about Sean."

Darcy was back on the track this week after recovering from a calf injury and eased into full training, with the club deciding it can better manage his workload in a WAFL practice game against West Coast on Saturday, rather than against the Crows.

Recruit Mason Cox has put together a strong pre-season and will give the Dockers the option to play star big man Luke Jackson as an onballer in their final pre-season hitout. 

Longmuir said Jackson had enjoyed a full summer training as a midfielder, learning the intricacies of the role with assistant coach Joel Corey. He will still have an impact, however, as a ruck and forward at times this year. 

"It's always been a plan to evolve him into that midfielder. He moves so well for a tall player, he's great at ground level, and he puts a lot of tackle pressure on for us in that role," Longmuir said.  

"We wanted to give him a full pre-season [in the midfield]. There's a fair bit of detail that goes around the stoppage aspect of the game, which he was learning in game, so it's been great to give him a pre-season where he's been able to learn some of those things when there hasn't been as much on the line. 

"Clearly there's going to be moments where he's really important for us in the ruck, and there's going to be times when we feel like he can best impact the game as a forward. 

"But he's matured as a player and he's really embraced the multiple roles. He wants to be a player where he can play where we need him and where he can impact the game. 

"To have that sort of flexibility is going to help us in games a lot."

Some coaches have expressed private concerns about how the new centre bounce rules, which prevent competing rucks from crossing the centre line before engaging, will impact the game. 

AFL general manager of football Greg Swann has said the League will discuss scenarios where rucks don't jump at the ball after Sydney big man Brodie Grundy drew a free kick by faking out opponent Nick Madden at a centre bounce on Thursday. 

"I've got some concerns, but not long-lasting concerns," Longmuir said.  

"I think it's going to take a little bit of time for the umpires to get their heads around the rule and how they adjudicate it, and I think we've seen a few iffy ones across the pre-season where the umps have been really helpful giving us advice and the detail around that.

"It's going to favour the jumping rucks maybe a little bit more, and I think it's going to bring back a little bit of nuance and ruck craft to the centre bounce, rather than just a big ruckman getting across the line and blocking the jumping ruckman. 

"I think it's going to bring a bit more craft and smarts to that area of the game … but I think all rucks will grasp it and be able to use it to their advantage."