Ziebell suffered an ankle strain against Adelaide last week and has been named by the Kangaroos, however coach Brad Scott told reporters at Arden Street on Friday that he still had some hurdles to overcome.
"He will have to do some more fitness testing over the next 24 hours," Scott said.
"He is a critical player for us in terms of the way we want to play over the weekend but also he's such an important player (in general). We will take no risks with him in terms of long-term damage.
"We will make a decision as late as we can."
And while the Bombers have endured a dreadful time of things off the field this week, Scott has spent the week reminding his players that on-field, Essendon's best can be as good as any team.
"We look at their best," he said. "Results can be misleading. Against Collingwood and Hawthorn they started well and their intensity was good.
"Essendon is still the quickest play-on team in the competition, even over the last month. Their contested marking, their run, ability to the ball into their attacking 50 is better than most and that's what we will be expecting on Saturday."
He expected the Bombers to be as galvanised as at any time this season and said their come-from-behind win over Fremantle earlier this year was an example of how well they play with their backs to the wall.
