Greenwood enjoyed a career-best year in 2014, fighting back from lean 2012 and 2013 seasons to finish third in North's best and fairest award, one vote behind winner Ben Cunnington.
Despite North's best efforts to re-sign the out-of-contract midfielder, Greenwood requested a move to Collingwood early in the trade period and the Roos reluctantly agreed.
Greenwood finished second at North for average possessions (25 a game) and inside 50s (4.2) in 2014, and third for contested possessions (10.4) and clearances (4). He was also one of the club's hardest runners both offensively and defensively.
But Ziebell told AFL.com.au from North's Utah training camp he was confident that the Roos could pick up Greenwood's slack.
"I don't think there will be an issue there. We've got a lot of young guys in that spot, guys like Trent Dumont, even Ben Jacobs, and older guys like 'Boomer' (Brent Harvey) and Leigh Adams can still go in there," Ziebell said.
"We've got a lot of guys who can go through the inside mid area, so we're pretty well stocked there.
"It's going to be a good opportunity for some young guys to come in and try to grab a spot."
Ziebell is one of 13 North players who arrived in Utah on Monday for a two-week high-altitude training camp.
The Roos' joint vice-captain is one of just three senior players on the camp, along with captain Andrew Swallow and Daniel Wells, with Jamie Macmillan, Brad McKenzie, Jacobs, Dumont, Shaun Atley, Luke McDonald, Mason Wood, Aaron Mullett, Kayne Turner and Joel Tippett joining them.
Like Swallow, Wells and Macmillan, Ziebell endured his share of injuries in 2014 and views the Utah camp as a chance to fast-track his 2015 pre-season.
Ziebell had post-season shoulder surgery, but will be able to run and do most of the skills work in Utah. However, he is still limited in the upper-body weights he can do and has to sit out game-sense drills, but hopes to resume full training shortly after the Christmas break.
Still, after struggling to complete full pre-seasons for much of his time at Arden Street, Ziebell is hopeful that this summer he can complete his second – largely – uninterrupted pre-season campaign in a row.
"Last pre-season was pretty successful, I got the majority of it done and I'm looking to build on that this year," Ziebell says.
"I might miss a little bit of football stuff, but as long as I can run I think that's the most important thing because my biggest area for improvement still is my fitness base.
"So I look forward to really working hard on that this year and building again, which is pretty exciting."
Despite playing some star cameos as a forward this year, Ziebell still sees himself as a midfielder.
Ziebell played a lot of football in attack as a junior and it showed in the way he took a career-high 14 contested marks in 2014 (double his next best tally, in 2013) and especially against Adelaide in round 22, when he kicked 4.5 in a best-on-ground performance.
The Roos' vice-captain enjoyed his time on the forward line and is happy to return there whenever coach Brad Scott asks.
But, ideally, he hopes to spend most of his time at the coalface in 2015.
"It's nice to know that you've got another string to your bow if things aren't working in the midfield," he added.
"But I still predominantly see myself as a midfielder and I really want to play the majority of my time in there."
