Coach Mark Harvey said Headland was only an outside chance for the early rounds after saying last week that he was 50-50 for round one.
“It's probably not even near that now," Harvey said from Fremantle Oval on Wednesday.
"He'd be in big doubt for round one now, probably round two or three at this stage.”
Headland, who was restricted to just six games last season with a serious knee injury, is yet to play this pre-season.
"It is [disappointing], because I think Des is probably in our top four from an importance point of view in our team. And he's a guy that can play midfield or forward,” Harvey said.
"Where our group's at, we need an experienced player like that playing as quickly as he can. And Des has grown very much in many ways, particularly leadership."
Luke McPharlin, Chris Mayne and Garrick Ibbotson will also miss this Saturday's NAB Challenge clash with Carlton in Bunbury, but Harvey said all three would be available for round one.
He plans to continue experimenting with players in different positions ahead of the season opener, with Chris Tarrant and Antoni Grover set to play a half at either end of the ground.
The rotating captaincy will also continue with Roger Hayden leading the side this week after Paul Hasleby, Michael Johnson and David Mundy had their chance.
Harvey said the experiment had been a success, particularly midfielder Mundy's reaction to his increased leadership responsibilities.
"[It's] pleasing to see how they react going forward once they've had a taste of that, and how they get around (Matthew) Pavlich and these sorts of guys and support that area of the game," Harvey said.
"That's why you have a look at sometimes where you put players in terms of positions of importance, and David's certainly grown in that area.
"He's sort of in our elite midfield group now."
Harvey said he would play a side as close to full strength as possible against Carlton and would use the hit-out as a rehearsal for round one against the Bulldogs.
"What you try and do, even though you're playing Carlton, is you still get ready for where your players might play in round one," he said.
"So there's still a little bit of an experiment in that particular way, when you're not necessarily playing against Carlton until later on in the year."
Dream Team watch – Des Headland is rated a $263,300 forward in Toyota AFL Dream Team 2009.
