Clark, 23, has been linked with offers from Greater Western Sydney and Fremantle among others, and is one of the final pieces of the Lions' puzzle for 2012.
The enigmatic forward/ruckman has played his last game for the season and will undergo knee surgery on Friday, which means he may have played his last game for the Lions if he decides to move on.
Voss said negotiations well under way, adding he was very optimistic of retaining Clark.
"We'll wait and see. We've stated our case of what we want. We've gone down the process of engaging, there's been dialogue that's happened, so it's just a matter of making sure that gets to the next step," Voss said.
"He's a required player here. You've got to have a good strong stable group coming together and that takes time, and I see some of those signs coming together.
"We've got a task in keeping that together but at the same time I think we're starting to see some genuine improvement, regardless of what happens in the next two weeks, from the group and what they're potentially capable of for the future."
The Lions have recently re-signed a host of youngsters, including Matthew Leuenberger, Daniel Rich, Tom Rockliff, Jared Polec, Patrick Karnezis and Ryan Harwood.
Clark - who also has an achilles injury - is the only change for Saturday night's match against West Coast at the Gabba and has been replaced by young forward Bryce Retzlaff.
Voss said the Lions could learn from the Eagles, who have rebounded from a disastrous 2010 to sit in the top four.
He said there was still a lot to play for over the final two rounds, starting with ruffling West Coast's feathers.
"Certainly we're very positive about finishing the season strong," Voss said.
"We're down a couple of players but I think the ones that have come in have provided enormous enthusiasm and life and they're looking for a way into this team in the future. If our intent is right we're a chance and I believe that in any contest."
Michael Whiting covers Brisbane Lions news for afl.com.au. Follow him on Twitter: @mike_whiting
