ALASTAIR Clarkson is the latest coach to tee off at the substitute rule being trialled in the NAB Cup, describing it as a "player welfare" issue as well as a major headache for coaching staff.

The Hawks have flown to Tasmania for Saturday's match against GWS without star players Lance Franklin, Sam Mitchell, Brad Sewell, Cyril Rioli and Jordan Lewis.

The Hawthorn coach says the interchange trial, and the ability to change players at half-time, has created a lot more work.

"The frustration's mainly been from the coaches, the amount of time we're spending throughout the course of the week just planning the amount of minutes that your players can play," he said.  

"Because with the sub rule, it means that either players are playing a lot of game time, or they're coming off at half-time, and not playing enough footy.

"That's the most difficult balancing act with players at this point of the season."

And in the wake of pre-season injuries at other clubs, Clarkson says "playing on hard surfaces" at NAB Cup venues adds to the concerns.

"It's a great danger period ... it's a very, very precarious six or eight weeks for all players," Clarkson said.  

"It is a very, very demanding time of the year, and I think over the last five or six years by round four there's usually eight to ten players [having] knee reconstructions.

"And that's our frustration as coaches, that this substitute rule actually limits the flexibility to manage your players as well as you'd like leading into round one.

"They'll pick up their loads over the next couple of weeks, and hopefully prepare us well for the Collingwood game round 1."

Matt Thompson is a reporter at AFL Media. You can follow him on Twitter @MattThompsonAFL