Longer, who was pick eight in the 2011 draft, has nominated Hawthorn as the club of his choice, but Kerr believes the Hawks would need to include pick 18 in their deal.
"He's had two years of development put into him and he's played nine senior games, I would've thought a trade would have to involve Hawthorn's first pick and potentially something else," Kerr said on Gillette Trade Radio.
The Lions have expressed interest in Hawthorn's Shane Savage but that would be separate to the Longer deal which is the first priority.
The club is bracing for a mass exodus of players including Longer, Sam Docherty, Elliot Yeo, Jared Polec and Patrick Karnezis, but are likely to keep James Polkinghorne.
But Kerr said that none of those players will be given away without appropriate compensation, and if a suitable trade could not be found then some of those players may need to re-evaluate their situation.
"I would expect that James Polkinghorne would probably stay a Brisbane player," Kerr said.
"With respect to the other boys, obviously they have expressed a desire to be traded, but we've got to actually get a trade done and if a trade isn't done then they'd have to sit back and reassess what their options are."
The Western Bulldogs, Carlton and Essendon have shown interest in trading for Victorian Sam Docherty, but given the Lions used pick 12 in the 2011 national draft to select the 19-year-old, the Bulldogs and Blues will need to put together an enticing offer.
"We have said to Carlton if you are genuinely interested in Sam then you need to put something on the table that we would be willing to consider," Kerr said.
"They've indicated there's a few players they are willing to trade but if it were Carlton we'd be trying to get the best draft pick we could. I don't think we'd look past the second-round.
"If it were to be Essendon it would have to involve players, but I would say Carlton and the Bulldogs are the two most likely at this point in time."
Yeo's bid to get to West Coast has been stalled by the fact that the Eagles have only offered a third-round pick in return for the 20-year-old who has played 27 games in his first two AFL seasons.
"We've been engaged with both Fremantle and West Coast and it's fair to say that West Coast led the running and were fairly proactive, but I think the fact that they've put a third-round pick on the table for a player in his second year who has played 19 games this year has left the door open for Fremantle.
“Fremantle have recognised that and have come to the fore to talk about something that might involve them," Kerr said.
As it stands at the moment Adelaide is in a better position than Port Adelaide to secure the services of Jared Polec.
"Both clubs are competing pretty keenly for Jared. If it were to be Adelaide it would have to involve players and we think we're going to have to bring a few players in, so that would be their strong suit," Kerr said.
"Pick 30 is what Port Adelaide has put on the table but it doesn't quite do it for us at this point."
Collingwood has shown the most interest in 21-year-old midfielder Patrick Karnezis but it will depend on the Magpies other trade deals.
Luke McGuane's bid to get to the Lions as a free agent is dependant on a number of factors, including the aforementioned negotiations as well as the future of star veteran Simon Black, who is weighing up a decision whether to continue for another year.
